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Kislorodning paramagnetizmi biologik ahamiyatga egami?

Kislorodning paramagnetizmi biologik ahamiyatga egami?


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Bu bizning eng keng tarqalgan kundalik O2 molekulasi a bo'ladi paramagnit biri (qarang: https://en.wikipedia.org/wiki/Oxygen).

Ammo buning biologik ahamiyati bormi? Boshqacha qilib aytganda, "tirik" deb hisoblangan har qanday mavjudotning fizik hajmida sodir bo'ladigan har qanday kimyoviy jarayonlar kislorodning paramagnit xususiyatlariga qandaydir tarzda, shakl yoki shaklda bog'liqmi?

(Menimcha, javob "yo'q" bo'lardi, lekin men bu sohada mutaxassis emasman!)


Qayta ifodalangan savolingizga javob

"Tirik" deb hisoblangan har qanday mavjudotning fizik hajmida sodir bo'ladigan har qanday kimyoviy jarayonlar kislorodning paramagnit xususiyatlariga qandaydir tarzda, shakl yoki shaklda bog'liqmi?

Bu ta'kidlangan "ha" va bu javobni bitta so'z bilan isbotlash mumkin: gemoglobin.

Poling va Koryell 1936 yilda kislorod-gemoglobin va CO-gemoglobindagi kislorod diamagnit ekanligini aniqladilar va men ushbu ajoyib maqolaning oxirgi xatboshidan iqtibos keltiraman:

Oksigemoglobin va uglerod-monoksigemoglobinda juftlashtirilmagan elektronlar mavjud emasligi magnit o'lchovlar bilan ko'rsatilgan; kislorod molekulasi, erkin holatda bo'lgan ikkita juftlashtirilmagan elektronga ega bo'lib, gemoglobinga biriktirilganda, shunga mos ravishda elektron tuzilishida chuqur o'zgarishlarga uchraydi.

Bu natija "vaqt sinovidan o'tdi" va gemoglobinning allosterik va kooperativ xususiyatlarini molekulyar darajada tushuntirishda asosiy kuzatuvdir. IMO, bu Paulingning ajoyib kuzatishlaridan biri bo'lib, uning ajoyib deduksiya kuchlarini ko'rsatadi.

Pauling ta'kidlaganidek, Faraday gemoglobinning magnit xususiyatlarini ham o'rganib chiqdi va o'zining daftariga "Yaqindagi suyuqlik qonini sinab ko'rish kerak" deb yozdi.

Yana Pauling va Koryelldan iqtibos keltirish uchun:

Agar u arterial va venoz qonning magnit sezuvchanligini aniqlagan bo'lsa, u ularni katta miqdorda farq qilgan bo'lardi (to'liq kislorodli va to'liq kislorodsiz qon uchun yigirma foizgacha); Bu kashfiyot, shubhasiz, katta qiziqish uyg'otdi va qon va gemoglobinni o'rganishga sezilarli ta'sir ko'rsatdi.


Rostini aytsam, bu kimyo imtihonidagi savolga o'xshaydi ... Yoki hech bo'lmaganda javob ... ya'ni O.2 paramagnit bo'lish ko'pchilik organik birikmalarning atmosfera kislorodi bilan tez reaksiyaga kirishishiga to'sqinlik qiluvchi "aylanish to'sig'ini" yaratadi:

O2 ning magnit xususiyatlari faqat laboratoriya qiziqishi emas; ular hayotning mavjudligi uchun mutlaqo hal qiluvchi ahamiyatga ega. Er atmosferasida 20% kislorod borligi sababli, barcha organik birikmalar, shu jumladan tanamiz to'qimalarini tashkil etuvchi moddalar, ekzotermik reaktsiyada H2O, CO2 va N2 hosil qilish uchun havo bilan tez reaksiyaga kirishishi kerak. Yaxshiyamki, biz uchun bu reaktsiya juda va juda sekin. Kislorod atmosferasidagi organik birikmalarning kutilmagan barqarorligining sababi shundaki, deyarli barcha organik birikmalar, shuningdek, H2O, CO2 va N2 faqat juftlashgan elektronlarga ega, kislorod esa ikkita juftlashtirilmagan elektronga ega. Shunday qilib, H2O, CO2 va N2 hosil qilish uchun O2 ning organik birikmalar bilan reaktsiyasi O2 dagi elektronlardan kamida bittasi reaktsiya paytida spinini o'zgartirishni talab qiladi. Bu katta energiya sarfini talab qiladi, bu to'siqni kimyogarlar aylanish to'sig'i deb atashadi.

(MakQuarri va Saymonning (bepul) Fizikaviy kimyo: Molekulyar yondashuv darsligidan iqtibos).


Mening fikrimcha, javob shunday yo'q.


Ommaviy magnit xususiyatlar atom/molekulyar (kimyoviy) xususiyatlarning natijasidir va kimyoviy reaktsiyalar odatda magnit xususiyatlarga bog'liq emas. o'z -o'zidan. Magnit xususiyatlar quyidagi hollarda rol o'ynashi mumkin:

  • Tashqi tomondan qo'llaniladigan magnit maydon mavjud (https://chemistry.stackexchange.com/q/24507/5295). Ba'zi bakteriyalarda magnitotaksis geo-magnit maydonga javoban bakterial harakatni boshqaradigan magnetit va gregit mikrokristallari tomonidan signalizatsiyani o'z ichiga oladi.
  • Reaktivlarning ba'zilari yoki reaksiya markazining tarkibiy qismlari magnit maydonni ta'sir qiladi (masalan, ferromagnit materiallar). Herve va boshqalar (1984) magnetit zarrachalarining qo'shilishi benzofenonning fotoreduksiyasi jarayonida ba'zi oraliq mahsulotlarning (yorug'likni yutuvchi vaqtinchalik) hosildorligini oshirishini ko'rsatdi.

Har holda, molekulyar kislorodning paramagenetizmi har qanday biokimyoviy reaktsiyaning omili ekanligini ta'kidlaydigan biron bir tadqiqotga duch kelmadim. Boshqa javobda ta'kidlanganidek, dioksidning barqaror triplet holati singlet holatiga nisbatan bir oz kamroq reaktivdir. Uchlik holati tufayli yuzaga keladigan paramagnetizm past reaktivlikning sababi emas. Boshqacha qilib aytganda, sabab va ta'sir munosabatlari yo'q.


Kislorodning paramagnetizmi biologik ahamiyatga egami? - Biologiya

Moda dietalar: biz hammamiz ular haqida eshitganmiz va hayotimizda bir yoki ikkitasiga amal qilganmiz. Ushbu parhezlar qat'iy qoidalarga ega va ko'pincha yog'lar yoki uglevodlar (uglevodlar) kabi ma'lum narsalarni iste'mol qilishda cheklovlar mavjud.

Ushbu turdagi dietani tanqidiy ko'rib chiqish uchun bir nechta narsalar mavjud. Birinchidan, odam o'z dietasidan barcha uglevodlarni chiqarib tashlashi mumkinmi? Eng muhimi, molekulalarning butun sinfini dietadan olib tashlash haqiqatan ham sog'lommi? Yog'lar haqiqatan ham muhim emas, to'g'rimi? Albatta, xolesterin yomon - to'g'rimi?

Uglevodlar yoki yog'lardan voz kechishga qaror qilishdan oldin, shuni bilishingiz kerakki, bu turdagi oziq-ovqatlar ularni hosil qiluvchi molekulalar turiga qarab nomlanadi. Keyin ular hujayralarda nima qilishlarini bilib olishingiz kerak.

Biologik makromolekulalar - bu hayot uchun zarur bo'lgan, kichikroq organik molekulalardan qurilgan katta molekulalar. Biologik makromolekulalarning to'rtta asosiy sinfi mavjud: uglevodlar, lipidlar, oqsillar va nuklein kislotalar (DNK va RNKda mavjud). Ularning har biri hujayraning muhim tarkibiy qismi bo'lib, juda ko'p funktsiyalarni bajaradi. Birgalikda bu molekulalar hujayra massasining ko'p qismini tashkil qiladi. Biologik makromolekulalar organikdir, ya'ni ular tarkibida uglerod mavjud. Bundan tashqari, ular vodorod, kislorod, azot, fosfor, oltingugurt va qo'shimcha kichik elementlarni o'z ichiga olishi mumkin. Biz har bir sinfni va ular bir-biri bilan qanday solishtirishni muhokama qilamiz.


Polar bo'lmagan funktsional guruhlar

Metil R-CH3

Metil guruhi yuqoridagi sinfimizdagi yagona qutbsiz funktsional guruhdir. Metil guruhi 3 ta vodorod atomiga bog'langan uglerod atomidan iborat. Ushbu sinfda biz ushbu C-H aloqalarini samarali qutbsiz kovalent aloqalar sifatida ko'rib chiqamiz. Bu shuni anglatadiki, metil guruhlari vodorod aloqalarini hosil qila olmaydi va suv kabi qutbli birikmalar bilan o'zaro ta'sir qilmaydi.

Chapda aminokislota izolösin, o'ngda xolesterin. Ularning har birida qizil rang bilan o'ralgan metil guruhi mavjud. Attribution: Mark T. Facciotti tomonidan yaratilgan (Erin Easlondan moslashtirilgan shaxsiy ish)

Yuqorida ta'kidlangan metil guruhlari turli xil biologik birikmalarda uchraydi. Ba'zi hollarda, birikma metil guruhiga ega bo'lishi mumkin, ammo qutbli xususiyatlarga ega bo'lgan boshqa funktsional guruhlar mavjudligi sababli umuman qutbli birikma bo'lishi mumkin (quyida muhokama qilinadigan Polar funktsional guruhlarga qarang).

Boshqa funktsional guruhlar haqida ko'proq bilib olsak, biz qutbsiz funktsional guruhlar ro'yxatiga qo'shamiz. Ogoh bo'ling!


Okeanlar va dengiz geokimyosi

6.10.2.5 To'g'ridan-to'g'ri atmosfera pCO2 Biologik nasosning imzosi

6.10.2.5.1 Organik uglerod nasosi

Biologik nasos CO ga birinchi darajali ta'sir ko'rsatadi 2 atmosferaning kontsentratsiyasi va shuning uchun erning iqlimi. Erigan CO ni olib tashlash2 fotosintez jarayonida er usti suvlaridan CO ning muvozanat parsial bosimi pasayadi2 ustki atmosferada (bu miqdor sifatida belgilanadi pCO2 er usti suvlari). Muzlik/muzlararolik uchun biologik nasosning qandaydir o'zgarishlari sabab bo'lishi mumkin pCO2 tsikllar (Pit va boshqalar., 1999). Biologik nasosning eng kuchli to'g'ridan-to'g'ri ta'siri pCO2 erigan CO ning er usti suvlarining kamayishi natijasida yuzaga keladi2 organik uglerod ("yumshoq to'qimalar" nasosi) ishlab chiqarish orqali.

Vaqt shkalasi. CO ning dengiz yuzasida kamayishi uchun vaqt shkalasi2 atmosferaga ta'sir qilish pCO2 Bu okeanlarni qayta tashkil etish va atmosfera / okean gaz almashinuvi muvozanati: yuzlab yillar davomida. O'tmishga nazar tashlasak, nasos yordamida biologik o'zgarishlar pCO2 Atmosfera holatida biz ushbu vaqt oralig'ida sodir bo'ladigan o'zgarishlarni qidiramiz (agar biologik nasosning samaradorligi bundan sekinroq o'zgarmasa).

Modelning sezgirligi. Eng so'nggi ajablantiradigan narsalardan biri bu atmosferaning sezgirligining kashfiyoti edi pCO2 biologik nasos juda modelga xosdir (Archer va boshqalar., 2000a Bacastow, 1996 Broecker va boshqalar., 1999). Xususan, okean kimyosining quti modellari sirkulyatsiya va kimyoning uzluksiz tasviriga asoslangan okean modellariga qaraganda biologik nasosning samaradorligiga nisbatan sezgirroqdir, ayniqsa, umumiy aylanish modellari (GCM) (3-rasm). Ushbu uchastkaning gorizontal o'qi jahon okeanining eng yuqori 50 m qismidagi PO 4 3 - shaklida erigan ozuqaviy fosforning inventarizatsiyasidir. Dengiz yuzasidagi fosforning zaxirasi fosforni quyidan ko'tarish va aralashtirish yo'li bilan etkazib berish va cho'kayotgan biogen zarralar sifatida olib tashlash o'rtasidagi muvozanatga bog'liq.

3-rasm. Atmosferaning barqaror holati modeli pCO2 okeanning eng yuqori 50 m qismida PO 4 3 inventarizatsiyasida ko'rsatilganidek, biologik nasosning samaradorligiga javob (manba Archer va boshqalar., 2000a).

Tafovutning sababi shundaki, dengiz yuzasida mavjud bo'lgan ozuqa moddalarining ko'pchiligi (fitoplankton samaraliroq yoki sirkulyatsiya kamroq energiya bilan tugashi mumkin) yuqori kengliklarda, xususan, Janubiy okeanda joylashgan. 1980-yillardagi hayratlanarli va muhim topilma shundan iborat ediki, yuqori kenglik yuzasidagi okeandagi ozuqa moddalari kontsentratsiyasining o'zgarishi oddiy turdagi okean kimyosi modellarida, quti modellari deb ataladigan bo'lsak, bu barqaror holatdagi CO ga nomutanosib ravishda katta ta'sir ko'rsatadi.2 atmosferaning kontsentratsiyasi (Knox and McElroy, 1984 Sarmiento and Toggweiler, 1984 Siegenthaler and Wenk, 1984). Past kenglikdagi sirt okeani, aksincha, unchalik samarali emas pCO2 atmosferadan.

Quti modeli oz miqdordagi okean suv havzalaridan iborat bo'lib, odatda uchdan bir necha o'ntagacha. Har bir quti bilan dengiz suvining kimyoviy xarakteristikalari bir hil (yaxshi aralashtirilgan) olinadi. Okeandagi suv oqimi Sv birliklarida berilgan qutilar orasidagi oqimlar sifatida tavsiflanadi (Sverdrups, 10 6 ms −1), ular odatda 100 Sv dan kam qiymatlarga o'zgaradi. Ikki quti orasidagi oqim o'zi bilan manba qutisining kimyoviy imzosini olib boradi, bu raqamli texnika "yuqori oqim" farqlash deb ataladi. Gaz almashinuvi CO kabi dengizdagi gaz konsentratsiyasini tortib olish uchun harakat qiladi2 va 14 CO2, atmosfera bilan muvozanat qiymatlari tomon. Qutilar orasiga o'rnatilgan oqimlar turli izlagichlarni, odatda 14 C, kuzatilgan qiymatlarga moslashtirish orqali aniqlanadi.

Biroq, yaqinda, GCMlar past kenglikdagi majburlashlarga nisbatan yuqori sezuvchanlikka ega ekanligi aniqlandi (Bacastow, 1996 Broecker). va boshqalar., 1999) va shuning uchun yuqori kenglikdagi majburlashga nisbatan past sezgirlik (Archer va boshqalar., 2000a). GCM okeanning kimyoviy va fizik maydonlarini doimiy ravishda, cheklangan farqlar tarmog'ida (diskretlangan) namunalar bilan ifodalashga qaratilgan. Tarmoq bo'ylab oqimlar inersiya, tortishish, stress, ishqalanish va Yerning aylanishi kuchlarini muvozanatlash orqali aniqlanadi. Chunki atmosfera pCO2 GCM dan yuqori qiymatlar yuqori kenglikdagi dengiz yuzasiga, atmosferadagi quti modellariga qaraganda kamroq sezgir. pCO2 yumshoq to'qimalar pompasiga ham kam sezgir bo'lib, ularning o'zgarishi ozuqa moddalarining mavjudligi bilan yuqori kengliklarga qaratilgan. Aksincha, CaCO ning ta'siri3 nasos GCMlarda quti modellariga qaraganda kuchliroq ko'rinadi (Matsumoto va boshqalar., matbuotda ), ehtimol CaCO3 ishlab chiqarish asosan issiq er usti suvlarida sodir bo'ladi. Qarama-qarshilik sabablari hali ham aniq emas. Kamonchi va boshqalar. (2000a) okeanning sirt qatlamlarida suvning turish vaqtida hukmronlik qiladigan vertikal diffuziyaga ishora qildi. Toggweiler (2003) er usti suvlarining, xususan, yuqori kengliklarda muvozanatlashuv darajasini ko'rsatadi. Quti modellari va GCMlar o'rtasidagi tafovut bartaraf etilmaguncha, haqiqiy okeanning yumshoq to'qimalarning biologik nasosidagi o'zgarishlarga sezgirligini taxmin qilish qiyin.

CaCO3 nasos. CaCO3 biologik nasosning tarkibiy qismi ham ta'sir qiladi pCO2 yer usti suvlari va shuning uchun atmosfera. CaCO3 ishlab chiqarish erigan karbonat ionining asosiy suvini yo'q qiladi, CO 3 2 - , bu aslida erigan CO ni harakatga keltiradi.2 reaktsiya tufayli konsentratsiyani oshiradi

CaCO3 nasosi shuning uchun oshirish uchun harakat qiladi pCO2 atmosferaning, kichik darajada, yumshoq to'qimalar pompasining ta'siriga qarshi. Bu paradoksal ko'rinadigan xatti-harakatlar karbonat tampon tizimining pH kimyosi natijasidir. Eritilgan CO2, uning gidratlangan shaklida H2CO3, kislotadir va u karbonat ioni, CO 3 2 -, H ning asos tuzi shakli bilan bufer kimyo muvozanatida mavjud.2CO3. CO 3 2 - ni kalsifikatsiya qilish orqali olib tashlash asosiy dengiz suvini kislotalaydi, karbonat tampon tizimining muvozanatini yuqori CO ga o'zgartiradi.2 diqqat. Bu jarayonning aksi CaCO ning erishi hisoblanadi3 fotoalbom yoqilg'i CO ning bosib olinishiga javoban dengiz tubida yoki marjon riflarida2 okeanga (Archer va boshqalar., 1989b, 1997 Uoker va Kasting, 1992). Marjon riflari ularni qurish uchun uglerod mavjudligi ortib borishi bilan kattalashishini oddiygina kutish mumkin, ammo pH muvozanati kimyosi erigan uglerodning mutlaq ko'pligini bekor qiladi.


Bioprotsess parametrlari va uni o'lchash

Ma'lumotlarni tahlil qilish va tegishli nazorat qilish uchun fermentatsiya/bio-qayta ishlash jarayonida (19.6-jadval) o'lchanadigan ko'plab fizik, kimyoviy va biologik parametrlar mavjud. Bioreaktorlarda o'lchovlarni amalga oshirish uchun ba'zi maxsus sensorlar ishlab chiqilgan. Barcha datchiklarning asosiy talabi shundaki, ular sterilizatsiya qilinishi kerak. Parametrlarni o'lchash (jadvalda keltirilgan) to'g'ridan-to'g'ri bioreaktorda yoki laboratoriyada amalga oshirilishi mumkin.

Bioprocessing jarayonida o'lchash mumkin bo'lgan muhim parametrlar:

O2 konsentratsiya (erigan)

Chiqindi gazlari kontsentratsiyasi (masalan, CO2)

Biologik parametrlar

Maxsus fermentlarning faolligi

Energetika (ATP kontsentratsiyasi)

Yuqori harorat (sterilizatsiya) bosimiga va mexanik stresslarga bardosh bera oladigan, ammo pH ni aniq o'lchaydigan pH elektrodlari mavjud. Kombinatsiyalangan elektrodlar (mos elektrod, shisha elektrod) qo'llaniladi. Aslida, elektrodlar bir nechta boshqa noorganik ionlarni o'lchash uchun ham mavjud.

Kislorod elektrodlari va CO2 elektrodlar O ni o‘lchash uchun ishlatilishi mumkin2 va CO2 mos ravishda konsentratsiyalar. Elektrodlar tabiatan amperometrikdir. Biroq, ular sterilizatsiya paytida shikastlanishga moyil. Ko'p ishlatiladigan texnikada O2 va CO2 mos ravishda O ning magnit xususiyati bilan o'lchanishi mumkin2 va CO ning infraqizil yutilishi2. Buni sensorlar yordamida amalga oshirish mumkin.

Mass-spektrometrdan foydalanish:

Mass-spektrometr ko'p qirrali texnikadir. U N ning kontsentratsiyasini o'lchash uchun ishlatilishi mumkin2, NH3, etanol va metanol bir vaqtning o'zida. Bundan tashqari, mass-spektrometr O.ning sifat va miqdoriy almashinuvi toʻgʻrisida maʼlumot olish uchun ham foydalidir2 va CO2.

Gaz o'tkazuvchan membranalardan foydalanish:

Bir vaqtning o'zida 8 tagacha erigan gazlarni o'lchash gaz o'tkazuvchan membranalar yordamida deyarli aniq amalga oshirilishi mumkin. Afzallik shundaki, bunday o'lchovni ozuqaviy muhitda amalga oshirish mumkin.

Kompyuterlardan foydalanish:

Kompyuterlar sanoat biotexnologiyasida ma'lumotlarni yig'ish, ma'lumotlarni tahlil qilish va fermentatsiya modellarini ishlab chiqish uchun ishlatiladi.

Fermentatsiya tizimida on-layn sensorlar va kompyuterlarni qo'llash orqali O kontsentratsiyasi haqida ma'lumot olish mumkin.2 va CO2, pH, harorat, bosim, yopishqoqlik, loyqalik, aeratsiya tezligi va boshqalar. Ba'zi boshqa parametrlarni (masalan, ozuqa moddalarining kontsentratsiyasi, mahsulot shakllanishi, biomassa kontsentratsiyasi) laboratoriyada, ya'ni oflayn o'lchovlarda o'lchash mumkin. Onlayn va oflayn o'lchovlardan to'plangan ma'lumotlar kompyuterga kiritilishi mumkin. Shu tarzda, fermentatsiyaga oid barcha ma'lumotlarni qayta ishlash, saqlash va olish mumkin.

Ma'lumotlarni tahlil qilish:

Kompyuterda to'plangan ma'lumotlar turli xil hisob-kitoblar uchun ishlatilishi mumkin, masalan. substratdan foydalanish tezligi, mahsulot hosil bo'lish tezligi, O2 qabul qilish va CO2 shakllanishi, issiqlik balansi, nafas olish koeffitsienti. Kompyuter ma'lumotlarini tahlil qilish orqali ma'lum bir fermentatsiya tizimi uchun optimal mahsuldorlikka erishish mumkin.

Fermentatsiya modellarini ishlab chiqish:

Kompyuter fermentatsiya jarayonlarining matematik modellarini ishlab chiqish uchun ishlatilishi mumkin. Ushbu modellar, o'z navbatida, yuqori mahsuldorlikka ega bo'lgan fermentatsiya tizimlarini iqtisodiy jihatdan samarali boshqarish uchun foydali bo'ladi.


Biologik molekulalar

Oziq-ovqat organizmni ozuqa moddalari bilan ta'minlaydi - uning yashashi uchun zarur bo'lgan materiya. Ushbu muhim oziq moddalarning ko'pchiligi shaklida keladi biologik makromolekulalar, yoki hayot uchun zarur bo'lgan katta molekulalar. Ushbu makromolekulalar kichikroq organik molekulalarning turli kombinatsiyalaridan qurilgan. Tirik organizmlar qanday maxsus biologik makromolekulalar turlarini talab qiladi? Ushbu molekulalar qanday hosil bo'ladi? Ular qanday funktsiyalarni bajaradilar? Ushbu bobda biz ushbu savollarni ko'rib chiqamiz.

Biologik makromolekulalarning to'rtta asosiy sinfi (uglevodlar, lipidlar, oqsillar va nuklein kislotalar) mavjud bo'lib, ularning har biri hujayraning muhim tarkibiy qismi bo'lib, juda ko'p funktsiyalarni bajaradi. Birgalikda bu molekulalar hujayra massasining ko'p qismini tashkil qiladi. Biologik makromolekulalar organikdir, ya'ni ular tarkibida uglerod atomlari mavjud. Bundan tashqari, ular vodorod, kislorod, azot, fosfor, oltingugurt va qo'shimcha kichik elementlarning atomlarini o'z ichiga olishi mumkin.

Ushbu molekulalar monomerlar deb ataladigan bo'linmalardan iborat. Biologik molekulalarning har bir turi turli monomerlardan tashkil topgan. Monomerlar bir-biriga kuchli kovalent bog'lar orqali zanjirga bog'langan. Kovalent bog'lanishlar monomerlarni bog'lashi muhim. Agar ular vodorod bog'lari bilan bog'langan bo'lsa, monomerlar bir-biridan osongina ajraladi va biologik molekula ajralib chiqadi. Agar monomerlarni ion bog'lari bog'lagan bo'lsa, biologik molekula suv bilan aloqa qilsa, parchalanishi mumkin edi.

1 -rasm Makromolekulaning tuzilishini marjon bilan solishtirish mumkin: ikkalasi ham zanjirga bog'langan kichik qismlardan qurilgan kattaroq tuzilmalardir. Makromolekulada “string” alohida bo'linmalarni bir-biriga bog'laydigan kuchli kovalent bog'lar bo'ladi. ("Daniel tomonidan “Springdagi munchoqlar”" CC BY-NC-ND 2.0 litsenziyasiga ega)


Kislorodning paramagnetizmi biologik ahamiyatga egami? - Biologiya

Gaz almashinuvi - Hayvonlar

I. Gaz almashinuvining ahamiyati
Nafas olish tenglamasini eslang: (CH2O)n + O2 CO2 + H2O + ATP (energiya)

II. Molekulyar harakat bo'yicha primer

A. Diffuziya va ommaviy oqim

  1. Kislorod va karbonat angidrid kabi gazlar diffuziya yo'li bilan mos ravishda organizmlarga kiradi va chiqadi. Diagramma kiritish

  2. Kislorod odatda hayvonlarga quyma oqim yoki boshqa faol mexanizm orqali kiradi (ya'ni., nafas olish, baliq gillalar bo'ylab suvni supurib, qurbaqa yutib yuboradi. Bu haqda quyida batafsilroq)

  3. Karbonat angidrid odatda ommaviy oqim bilan chiqariladi

Uyga olib boriladigan darslar: Bu tenglama bizga ma'lum bir molekula uchun diffuziya tezligi ekanligini aytadi :

III. Fik qonunining biologik oqibatlari: katta sirt maydoni (A) majburiy, shart
Ushbu muammoni hal qilish uchun turli xil echimlar mavjud. Asosiy xususiyat - gaz almashinuvi uchun umumiy sirtni oshirish (kislorodni qabul qilish, karbonat angidridni yo'qotish). Bu sirt-hajm nisbatlarining yana bir yaxshi namunasidir. Biz bilib olganimizdek, ma'lum bir hajm uchun sirt maydonini oshirish uchun filament yoki tekislangan shakl eng yaxshi shakl bo'lib, organizmlar buni qanday amalga oshiradilar:

Qiziqarli aylanma yo'l Gaz almashinuvi va s/v nisbati haqidagi bilimlaringizga asoslanib, nega ulkan hasharotlar kino ijodkorining tasavvuridan iborat ekanligini tushuntiring.


IV. Fik qonunining biologik oqibatlari: qisqa diffuziya masofasi bo'lishi kerakce (L)
Atrof muhit va organizm ichida qisqa diffuziya masofasi bo'lishi kerak. Fik qonuni bizga diffuziya tezligi masofaga teskari bog'liqligini aytadi - masofa qanchalik katta bo'lsa, diffuziya tezligi shunchalik sekin bo'ladi. Aslida, diffuziya uzoq masofalarda og'riqli tarzda sekinlashadi. Ammo, qanchalik sekinroq? Keling, glyukoza stavkasini hisoblaylik:

Bu erda glyukoza uchun hisob-kitoblarni kiriting

Uy saboqlarini oling: gazni yutuvchi sirt qalinligi bir necha hujayradan oshmaydi (masalan.. gubkalar, o'pkalar, dengiz bodringlari, markaziy bo'shlig'i suyuqlik bilan yuvilgan gidra naychalari, gubkalar - ko'plab kamerali barglar tekis, ingichka)


V. Fik qonunining biologik oqibatlari: Katta sirt maydoni katta maydonni ta'minlaydi Quritish.
Paradoks moddalar almashinuvi uchun gazlar almashinuvi uchun hayvonlar (va o'simliklar) katta sirt maydoniga ega bo'lishi kerak, degani, suv yo'qotadigan joylar ham ko'payadi.


VI. Fik qonunining biologik oqibatlari: gazlarni olish yo'li bo'lishi kerak the yutuvchi sirt

A. Musbat bosimli nafas olish
Qurbaqalar - havoni tomoqqa, pastki tomoqqa - havo kiradi - tomoqqa tushirish uchun yuqoriga ko'tariladi (= ommaviy oqim)


Fil Kallaxan Paramagnetizm kuchi haqida

Men bu hodisani pinhole kamera deb ataladigan 200 dollarlik asbob bilan ko'rsata olaman. Siz shunchaki linza qopqog'ida teshik qazasiz va to'liq zulmatda kameraga tosh yopishtiring. Uch hafta ichida siz kamalakning har bir rangi bilan chiroqlarni ko'rsatadigan filmni ishlab chiqishingiz mumkin. Fotonlar juda oz miqdorda chiqadi, uni olish uchun uni uch hafta davomida o‘sha yerda qoldirish kerak, lekin plyonka yorug‘likka sezgir va agar u yerda yetarlicha uzoq vaqt qoldirsangiz, suratga tushasiz. Bu paramagnit tog' jinslarining yorug'lik hosil qilishining rad etib bo'lmaydigan dalilidir. Esda tutingki, o'simlik ildizlari uchtasi uchun mavjud

Fil: Xo'sh, bu holatda men uning ishlayotganini bilardim, lekin uning qanday ishlashi mexanizmini topishim kerak edi. Mening ba'zi eksperimental ishlarim o'simliklarning samaradorligini sezilarli darajada oshirishni taklif qiladi. Misol uchun, men paramagnit darajasi 60 cg [santimetr-gram-sekund] bo'lgan qumli tuproqlarda o'stirilgan javdarni oldim va bu tuproqlarni paramagnit jinslar bilan oziqlantirdim. Javdar, davolashdan oldin, ildizlarida 10-15 azotli tugunlar bo'lsa, davolashdan keyin ularning soni 200 tagacha ko'paydi. Bu shuni ko'rsatadiki, tuproqdagi bakteriyalar ushbu paramagnit kuchsiz minerallarni o'simlik mavjud bo'lgan shaklga aylantira olmaydi. Ular hech qachon paramagnit kuchsiz o'g'itlarni ishlatmaydilar. Xlorofill uchun yorug'lik qanday bo'lsa, bu kuch ildizlarga tegishli. Agar sizda yorug'lik bo'lmasa, xlorofill ishlay olmaydi. Agar sizda paramagnit kuch bo'lmasa, unda ildizlar ishlamaydi.


Kislorodning biokimyoviy talabi va suv sifati

Kislorodning biokimyoviy talabi (BOD) organik moddalarning oksidlanishida mikroorganizmlar (masalan, aerob bakteriyalar) tomonidan ishlatiladigan kislorod miqdorining o'lchovidir. Organik moddalarning tabiiy manbalariga o'simliklarning chirishi va barglarning tushishi kiradi. Biroq, oziq moddalar va quyosh nurlari inson ta'siri tufayli haddan tashqari ko'p bo'lsa, o'simliklarning o'sishi va chirishi g'ayritabiiy ravishda tezlashishi mumkin. Ko'chalar va yo'laklardan uy hayvonlari chiqindilari, maysazor o'g'itlari barglari, o't parchalari va turar-joylardagi qog'ozlardan oziq moddalar olib yuradigan shahar oqimi kislorodga bo'lgan talabni oshirishga yordam beradi.

Parchalanish jarayonida iste'mol qilinadigan kislorodning ko'payishi boshqa suv organizmlarini yashashi uchun zarur bo'lgan kisloroddan mahrum qiladi. Shu sababli, past erigan kislorod darajasiga ko'proq bardoshli organizmlar omon qolish uchun kislorodga (aerobik) muhtoj bo'lgan turli xil tabiiy suv tizimlarining o'rnini bosishi mumkin. Bu organizmlar parchalanish tsiklining bir qismidir va ular o'lik suv o'tlari va boshqa o'lik organizmlar bilan oziqlanadi.

Keling, suv tizimlarida kislorod aylanishini to'liqroq ko'rib chiqaylik. Tsiklning boshida suv o'tlari va boshqa ishlab chiqaruvchilar noorganik ozuqa moddalarini o'zlashtiradilar va ularni organik to'qimalarni qurish jarayonida foydalanadilar. Baliq va boshqa suv hayvonlari kabi iste'molchilar ishlab chiqaruvchilarning bir qismini iste'mol qiladilar va ozuqa moddalari oziq-ovqat zanjirida yuqoriga ko'tariladi. Ushbu organizmlar nobud bo'lganda, bakteriyalar organik birikmalarni parchalaydi va suvga nitrat, fosfat, kaltsiy va boshqalar kabi noorganik ozuqa moddalarini chiqaradi. Ushbu oziq moddalarning ba'zilari quyi oqimga yoki cho'kindilarga tushadi, lekin ularning aksariyati qayta-qayta qayta ishlanadi. Suvli suv ustunidagi bakteriyalarning aksariyati aerobdir. Bu shuni anglatadiki, ular metabolik jarayonlarni amalga oshirish uchun kisloroddan foydalanadilar. Esda tutingki, biz boshqa tegishli mashqlarda normal sharoitda erigan kislorod juda past konsentratsiyalarda mavjudligini bilib oldik. Suv tizimlarida kislorodning tabiiy darajasi har doim aerob bakteriyalar faolligining normal darajasi bilan bir oz kamayadi. Ko'pgina hollarda, agar erigan kislorod konsentratsiyasi millionda 5 qismdan (ppm) pastga tushsa, baliq juda uzoq vaqt yashay olmaydi. Alabalık yoki qizil ikra kabi barcha toza suv turlari bu darajadan ancha yuqori darajada nobud bo'ladi va hatto baliq va sazan kabi kam kislorodli baliqlar 5 ppm dan pastroq xavf ostida bo'ladi.

Aerob bakteriyalar faolligining anormal darajada yuqori bo'lganida, erigan kislorod darajasi keskin pasayishi mumkin. Bunday o'zgarishlar qanday sharoitlarda sodir bo'ladi? Odatda, bu g'ayritabiiy bakteriyalar faoliyati tizimga qandaydir g'ayritabiiy "ifloslanish" kiritilganda sodir bo'ladi. Bu maishiy kanalizatsiya, septik tankning oqishi va o'g'it oqishi kabi manbalar uchun organik ifloslanish shaklida yoki ifloslangan texnogen mahsulotlar kabi maishiy yoki sanoat manbalaridan noorganik moddalar shaklida bo'lishi mumkin. Organik birikmalarning tabiiy manbalari suv tizimlariga toshqinlar, ko'chkilar va eroziya orqali ham kirishi mumkin.


Gipoksiyaga moslashish

Birinchi gipoksiya va HIF tomonidan boshqariladigan genlardan biri aniqlangan EPO gen. Gematokritning ortishi gipertenziya va tromboemboliya bilan bog'liq bo'lsa, yuqori balandlikda yashovchi odamlar eritrotsitlar darajasining oshishini qoplaydi. Maks Gassman (Tsyurix universiteti) haddan tashqari ifodalangan transgen sichqonlar avlodini tasvirlab berdi EPO gipoksiyadan mustaqil ravishda va 0,8 dan 0,9 gacha gematokritga ega bo'lgan, bu yovvoyi turdagi sichqonlarda topilganidan deyarli ikki baravar ko'p (Vogel va boshq. 2003). Kutilmaganda, bu sichqonlarda splenomegaliya namoyon bo'lgan bo'lsa-da, qon bosimi, yurak urish tezligi yoki yurak chiqishi ortishi kuzatilmadi. Ushbu transgen sichqonlarning yuqori gematokrit darajasiga moslashishi eritrotsitlar moslashuvchanligini oshirish orqali qonning viskozitesini tartibga solinadigan ko'tarilishi natijasidir. Qizig'i shundaki, EPO ning haddan tashqari ekspressiyasi sichqonlarni miyokard infarktidan va yorug'likdan kelib chiqqan retinal degeneratsiyadan himoya qildi. EPO transgen sichqonlari, shuningdek, skelet mushaklaridagi kapillyar zichlikning ortishi tufayli uzoqroq suzadi va uzoqroq yuguradi, ammo nerv-mushak birikmalari kamaygan. Bu gipoksiyadan mustaqil EPO Transgen sichqoncha modeli yuqori EPO darajalariga moslashishning fiziologik oqibatlarini tushunishda ibratli bo'ldi.

Jeff Arbeit (Vashington universiteti) terining haddan tashqari ifodalanishiga moslashish qobiliyatini o'rgandi. HIF-1kislorod degradatsiyasi domeniga (ODD) ega bo'lmagan a gen. Ushbu tajribalarning maqsadi a ning ta'sirini tushunish edi HIF-1a epiteliy to'qimasini differensiallashda funktsiyaning ortishi. U yaratgan K14-HIF-1a G'alati HIF ni o'zlarining bazal keratinotsitlarida konstitutsiyaviy ravishda ifoda etgan transgenik sichqonlar (Elson va boshq. 2001). Sichqonlarda mikrotomirlarning ko'payishi tufayli terisi qizargan bo'lsa-da, VEGF kabi HIF-1 maqsadli genlarining haddan tashqari ifodalanishiga qaramay, terida hech qanday aniq fenotip aniqlanmadi. Aslida, teri K14-HIF-1aG'alati sichqonlar, shuningdek, shox pardalar, VEGF mRNKning doimiy ko'tarilishi bilan bog'liq bo'lgan neonatal qon tomirlarini kesishning muvaffaqiyatsizligi tufayli oqishga chidamli ekanligi aniqlandi. Ushbu natijalar shuni ko'rsatadiki, keratinotsitlarda HIF-1a ning konstitutsiyaviy ifodasi angiomaga o'tmaydigan gipervaskulyarlikka olib keladi. Qizig'i shundaki, xuddi shu transgen sichqonlarni DMBA / TPA bilan davolash natijasida hosil bo'lgan papillomalar hajmi va soni kamayadi. Biroq, 16-27 haftadan so'ng, hosil bo'lgan papillomalar ko'proq invaziv bo'lib, HIF-1 teri saratoni rivojlanishining kech bosqichi omili ekanligini ko'rsatadi.

Moyaklarning seminifer kanalchalari yomon qon tomirlangan va past kislorodli kuchlanish ostida. Roland Venger (Syurix-Irxel universiteti) bir romanni tasvirlab berdi HIF-1a izoformi, hHIF-1aTe deb ataladi, u faqat inson moyaklarida ifodalanadi (Depping va boshq. 2004). Prognoz qilingan kodlash hududida N-terminal bHLH domenining 59 ta aminokislotasi yo'q, bu hHIF-1a ning dominant-salbiy funktsiyasiga olib keladi. U normal HIF-1 funktsiyasining dominant-salbiy regulyatorining moyakga xos ifodasi HIF-1 tomonidan transkripsiya bilan tartibga solinadigan genlar kichik to'plamini inhibe qilishda ishtirok etishi mumkinligini taklif qildi. Ko'pgina glikolitik fermentlarning moyaklar uchun o'ziga xos variantlari faqat spermatogenez jarayonida namoyon bo'lganligi sababli, normal HIF-1 funktsiyasini inhibe qilish HIF-ning transkripsiyaviy nazorati ostida bo'lgan glikolitik fermentlarning hamma joyda mavjud izoformlari ekspressiyasining pasayishiga yordam berishi mumkin. 1. Dominant-salbiy regulyatsiya orqali transkripsiya faolligini inhibe qilish moyakda keng tarqalgan mexanizmdir (masalan, Id oqsili). Roland Venger shuningdek, moyakda yuqori darajada ifodalangan PASKIN (Katschinski va boshq. 2003) bo'lgan yangi, sutemizuvchilarning PAS domen oqsilini muhokama qildi. Biroq, moyaklarda qanday fiziologik rol o'ynashi aniq emas.

Stella Kourembanas (Garvard tibbiyot maktabi) gipoksiya vazokonstriksiyani va o'pka tomirlarining tomir devorini qayta qurishni rag'batlantiradigan dalillarni taqdim etdi, bu o'zgarishlar o'pka gipertenziyasiga yordam beradi. Gipoksiya qon tomir silliq mushak hujayralarining mitogenlarga proliferativ javobini oshiradi va telomeraza faolligini oshirish orqali ularning umrini uzaytiradi (Minamino va Kourembanas 2001). Gipoksiya, shuningdek, qisman NF-kB tomonidan makrofag yallig'lanish oqsilining transkripsiyaviy induktsiyasi orqali o'pkada yallig'lanish hujayralari infiltratsiyasini keltirib chiqaradi. O'pkaning gipoksiyaga moslashishi gem oksigenaza genini induktsiya qilish orqali amalga oshiriladi.HO-1), uning mahsuloti antioksidant bilirubin va vazodilatator uglerod oksidini hosil qiladi (Minamino va boshq. 2001). Kourembanasning tadqiqotlari shuni ko'rsatdiki, HO-1 ishlab chiqarish uchun genetik jihatdan o'zgartirilgan hujayra chiziqlari va sichqonlar gipoksiyaga duchor bo'lganda proliferatsiya va yallig'lanishning kamayganligini ko'rsatdi. Ushbu tadqiqotlar o'pka to'qimalarining gipoksiyaga moslashishiga imkon berish uchun HO-1 ning farmakologik manipulyatsiyasi uchun muhim ahamiyatga ega.

Larissa Shimoda (Jons Xopkins tibbiyot maktabi) 3 hafta davomida 10% kislorod ta'siriga uchragan kemiruvchilarda o'pka tomirlari silliq mushaklarining qisqarishi va ko'payishi paytida o'pka arterial bosimida ion gomeostazining rolini o'rgandi (Raj va Shimoda 2002). U bu hayvonlarning pulmoner silliq mushak hujayralari zaiflashgan kuchlanishli K+ (Kv) kanal faolligini, membrana potentsialining depolarizatsiyasini, tinch holatda hujayra ichidagi Ca2+ va hujayra ichidagi pH ning ishqoriy siljishini ko'rsatishini aniqladi. Kv kanali faolligi va membrana depolarizatsiyasining inhibisyonu Kv kanali ekspressiyasining pasayishi natijasidir, pH ning ishqoriy siljishi esa Na+/H+ almashinuvchi ifodasi va faolligining oshishi natijasidir.

Ivan McMurtry (Kolorado sog'liqni saqlash fanlari markazi universiteti) o'pka gipertenziyasida doimiy o'pka vazokonstriksiyasi vositachiligida kichik GTP-bog'lovchi RhoA proteini va uning quyi oqim effektori Rhokinazning rolini muhokama qildi (McMurtry va boshq. 2003). U 3 haftalik hipobarik kislorodga (10% kislorod) ta'sir qilgan kalamushlarni Rhokinase inhibitori Y-27632 bilan davolash o'pka tomirlarining qarshiligini va NO sintezini inhibe qilish natijasida yuzaga kelgan vazokonstriksiyani to'liq bartaraf etishini aniqladi. Agar kalamushlar bir vaqtning o'zida Y-27632 bilan davolash paytida gipoksiyaga duchor bo'lgan bo'lsa, o'pka gipertenziyasi, qon tomirlarini qayta qurish va o'ng qorincha gipertrofiyasining og'irligi kamaydi. Biroq, tizimli arterial bosim o'zgarmagan. Ushbu tadqiqotlar shuni ko'rsatadiki, Rho kinaz signalizatsiyasi ion kanallari gomeostazidagi o'zgarishlar bilan birga o'pka gipertenziyasiga ham hissa qo'shadi va Rho kinaz signalizatsiyasining inhibisyonu, qisman, gipoksiya tufayli kelib chiqqan o'pka gipertenziyasining oqibatlarini engillashtirishi mumkin.

Frank Giordano (Yale University) investigated the role of HIF-1 in adaptive changes in oxygen delivery to the myocardium. Using cardiac specific deletion of HIF-1α, he found that the mice were viable, but have cardiac dysfunction at basal normoxic conditions, and reduced cardiac vascularity (Huang et al. 2004). Furthermore, the rate of developed pressure and relaxation were substantially reduced in HIF-1α-deficient hearts when compared with wild-type counterparts. These findings correlated with reduced contractility at the cardiac myocyte level and prolongation of calcium transients. Metabolically, HIF-1α-deficient hearts generated less ATP under normoxic conditions and exhibited reduced expression of numerous HIF-1 target genes. In contrast to HIF-1α deficient hearts, deletion of VHL in the heart resulted in 100% mortality by 5 mo of age, which was associated with hypervascularity and myocyte loss and replacement fibrosis. The increased fibrosis correlated with increased levels of TGFβ1. These results demonstrate the importance of regulated HIF-1 expression in cardiac myocytes under normoxic conditions.

Kenneth Walsh (Boston University) explored the protective role of Akt using a transgenic mouse system in which Akt could be conditionally activated in cardiac myocytes (Fujio et al. 2000 Miao et al. 2000). He found that short-term activation of Akt resulted in reversible hypertrophy and cardioprotection when the heart was challenged by stress. However, prolonged Akt expression induced severe cardiac hypertrophy and ventricular remodeling. Thus, in considering genetic or pharmacological approaches to use Akt for treatment of heart disease, only short-term treatments may prove beneficial, with chronic treatment, leading to heart failure.

Using a hypoxia-specific marker, Ernestina Schipani (Massachusetts General Hospital) showed evidence that the fetal chondrocytic growth plate (central region) contains a hypoxic region, and also stains positive for HIF-1α (Schipani et al. 2001). Yo'qotish HIF-1α expression in chondrocytes results in shortened limbs and a malformed sternum with no clear cellular element. Loss of HIF-1α causes increased cell death in the chondrocytic growth plate. Cells that lack HIF-1α in the interior of the growth plate die by apoptosis and fail to undergo growth arrest. VEGF expression in the growth plate is regulated through both HIF-1α-dependent and HIF-1α-independent mechanisms. Surprisingly, VEGF expression is elevated in a HIF-1α-independent manner in chondrocytes surrounding areas of cell death, and this, in turn, induces ectopic angiogenesis. HIF-1α-null chondrocytes are also unable to maintain ATP levels in hypoxic microenvironments, indicating a fundamental requirement for this factor in the regulation of chondrocyte metabolism. Thus, HIF plays multiple roles in chondrocyte development by providing growth arrest and survival signals that allow chondroblasts to adapt and differentiate in a hypoxic environment.

Mammalian lenses are avascular throughout most of life, but continue to grow in a hypoxic environment, indicating that they have adapted to a low-oxygen environment. David Beebe (Washington University) presented results from experiments, in which he investigated the role of oxygen in regulating lens growth in vivo. He found that young rats exposed to 60% oxygen compared with normoxic conditions exhibited little change in proliferation as assayed by BrdU labeling. In older rats, BrdU labeling was low under normoxic conditions, but increased to the same level as the younger rats upon exposure to hypoxia. At the cellular level, the rate of lens-fiber cell production also increased in rats exposed to 60% oxygen. Again, HIF-1 seems to play an important role in lens development and adaptation to hypoxia, as HIF-1α-deficient lens showed severe disruption of epithelial and fiber cell morphology and degenerated postnatally. In younger rats, hypoxia has little effect on epithelial proliferation or lens growth. In older rats, hypoxia is essential in inhibiting epithelial proliferation and lens growth. How HIF inhibits proliferation in the aging lens could provide insight into the tissue-specific effects of HIF on growth regulation and adaptation to a low-oxygen environment.

Gregg Semenza discussed the importance of physiologic responses to hypoxia that are mediated by the transcriptional activator HIF-1 and its downstream targets (Semenza 2004). He gave a variety of examples of the importance of HIF1 cardiorespiratory physiology. For example, in mice with loss of one HIF-2α allele, hypoxia-induced expression of endothelin-1 and norepinephrine is significantly reduced, and these mice fail to develop pulmonary hypertension after four weeks of exposure to 10% oxygen. In mice with loss of one HIF-1α allele, the carotid body is unable to properly signal a response to reduced oxygen conditions. In mice with loss of one HIF-1α allele, intermittent hypoxia does not induce EPO production or cardiac protection when compared with wild-type mice with two functioning HIF alleles. He also presented experimental data that EPO provides potent protection against ischemia-reperfusion injury in the heart. These results further support an important, but yet complex role for HIF in maintaining normal tissue homeostasis in response to changing oxygen conditions.

Hypoxia, HIF, and oncogenesis

A major question regarding HIF is its role in oncogenesis. Adrian Harris (Oxford University) reported that head and neck cancer patients negative for HIF-2α and carbonic anhydrase IX (CAIX) had the best prognosis from the analysis of the European CHART trials, suggesting that the combination of the two molecular markers may be useful for prognosis in the future (Potter and Harris 2004). Amato Giaccia (Stanford University) reported that HIF itself did not act as a classical oncogene, in that it could not transform NIH 3T3 cells or melanocytes in vitro. However, overexpression of an ODD-deficient HIF-1 increased transformation and tumor growth of mouse cells. To date, no gain-of-function mutations in HIF that make it stabilized under aerobic conditions or increase its transactivation potential have been identified in tumor cells. Gregg Semenza presented additional evidence that overexpression of HIF-1α enhanced the growth of transplanted tumors in immune-deficient mice, and that inhibition of HIF through the use of dominant-negative HIF inhibited tumor growth (Semenza 2003). Frank Lee (University of Pennsylvania) reported that proline 582 to serine polymorphism that is found at a frequency of 0.073 in the population did not affect HIF hydroxylation or transactivation. Whereas HIF itself does not seem to be mutated in pathological disorders or neoplastic cells, a variety of other factors that affect HIF stability are dysregulated or inactivated. Cell lines derived from tumors that have lost the VHL tumor-suppressor gene display aerobic HIF-1α protein expression (Maxwell et al. 1999 Ohh et al. 2000). Tumors such as renal cell carcinomas (RCC) that possess mutations in VHL also exhibit high aerobic expression of HIF-1-regulated genes, whereas reintroduction of wild-type VHL substantially reduces the aerobic level of HIF-1α protein to those found in untransformed or transformed cells that express wild-type VHL. Bill Kaelin (Dana-Farber Cancer Institute) presented data that indicates that a HIF-2α variant lacking both of its two prolyl hydroxylation/pVHL-binding sites prevents tumor inhibition by pVHL in a DNA-binding-dependent manner (Kondo et al. 2003). Furthermore, inhibition of HIF-2α expression with short hairpin RNAs is sufficient to suppress tumor formation by pVHL-defective renal carcinoma cells (Kondo et al. 2003). These results strongly argue that tumor suppression by pVHL is tightly associated with the regulation of HIF protein.

Other pathways were discussed by Bill Kaelin that impact HIF activity by affecting TOR activity. For example, loss of the tuberous sclerosis complex tumor-suppressor gene (TSC-2) results in hamartomas. Mutant versions of TSC-2 have little effect on mTOR and HIF accumulation, whereas wild-type TSC-2 inhibits mTOR and HIF accumulation (Brugarolas et al. 2003). Wayne Zundel (University of Colorado Health Sciences Center) reported that CSN5 subunit of the COP9 signalsome holocomplex interacts directly with both the CODD (independent of prolyl-hydroxylation state) and the pVHL E3 ligase. He concluded that CSN5, pVHL, and the PHDs interact with the same region of HIF-1α, and therefore, CSN5 alters pVHL or PHD affinity for HIF-1α under aerobic conditions (Bemis et al. 2004).

Exploiting tumor hypoxia

Over the last decade, numerous preclinical and clinical studies have indicated that hypoxia is an important indicator of therapeutic response to radiotherapy, chemotherapy, and even surgery. It decreases the effectiveness of radiation that requires free radicals to kill cells, makes them refractory to killing by chemotherapy agents that require rapidly proliferating cells to be effective, and selects for tumor cells that are highly aggressive. Peter Vaupel (University of Mainz) discussed the mechanisms leading to tumor hypoxia (Vaupel 2004). He stated that there are three major mechanisms that cause tumor hypoxia: (1) the inability of the structurally abnormal vessels in the tumor to perfuse tumor cells adequately (2) interrupted microcirculation, and (3) tumor or therapy-induced anemia. Additional contributory mechanisms include carboxyhemoglobin (HbCO) formation in heavy smokers and hypoxemia in microvessels arising from the venous side of the vascular network. In the new age of targeted therapy, pretreatment assessment of hypoxia in patients with solid tumors could allow them to benefit from the addition of a hypoxia directed therapeutic.

Currently, a variety of strategies exist to exploit tumor hypoxia for treatment. Dietmar Siemann (University of Florida) discussed a number of these strategies they include overcoming tumor hypoxia through the administration of agents such as EPO, exploiting tumor hypoxia through the use of bioreductive agents that are activated under hypoxic conditions, and increasing tumor ischemia through the use of vascular targeting agents. He discussed treating malignant disease by targeting the blood vessel support networks of tumors, a topic that has received a great deal of attention in recent years, albeit more from the antiangiogenic side than from the vascular targeting side. Vascular targeting agents differ from anti-angiogenic agents, in that they destroy established vasculature (Siemann et al. 2004). Preclinical studies have demonstrated that vascular targeting agents can produce rapid and significant vascular effects that, once initiated, lead to widespread, dose-dependent tumor necrosis in a matter of hours or days. Whereas these agents seem to be highly effective in reducing tumor size, they alone do not eradicate tumors, as tumor cells that can obtain their oxygen and nutrients by diffusion could survive and repopulate the tumor. Therefore, a vascular targeting agent should be combined with radiotherapy or chemotherapy to improve tumor response. In early Phase I and Phase II clinical trials, vascular targeting agents have exhibited the ability to produce significant reductions in tumor blood flow at acceptable doses. The future for these agents looks promising.

Martin Brown (Stanford University) described one mechanism by which a nontoxic prodrug can be activated to a toxic drug under hypoxic conditions, as a model for hypoxia specific cytotoxins. (Brown and Wilson 2004) He stated that molecules that can undergo one-electron reduction to a radical can be reoxidized to the original compound under normoxic conditions, but will not be reoxidized under hypoxic conditions, and thus will retain their ability to induce DNA damage. One example of a drug that is activated under hypoxic conditions is Tirapazamine (TPZ). TPZ potentiates the antitumor effect of radiation by selectively killing the radiation-resistant hypoxic cells in tumors. It also enhances killing of hypoxic tumor cells treated with cisplatin. Whereas a Phase-III study with cisplatin-based chemoradiotherapy is now underway, the dose of TPZ that can be administered during chemoradiation is limited by the side effects of neutropenia. Thus, whereas the concept has been demonstrated to work, new hypoxia-activated prodrugs are needed. Martin Brown also discussed clostridial-dependent enzyme prodrug therapy (CDEPT). This approach relies on the spore form of clostridia germinating in the hypoxic/necrotic regions of solid tumors and releasing the prodrug-activating enzyme in areas of the tumor that have hypoxic tumor cells and far from blood vessels. Obviously, there would be a potential advantage to combine vascular targeting therapy that would increase tumor necrosis and hypoxic with CDEPT.

Hypoxia-targeted therapies such as clostridia or TPZ act to kill hypoxic cells in a nonselective manner. Giovanni Melillo (National Cancer Institute) described a recent screen of 2000 compounds that represent a “Diversity Set” of the NCI's repository to identify HIF inhibitors (Rapisarda et al. 2002). This screen was instrumental in demonstrating that pharmacological inhibitors of HIF-1α could be screened in a high-throughput fashion, and attempted to exclude compounds that were cytotoxic, on the basis of the changes in expression of a second, constitutively expressed luciferase reporter gene. One group of compounds that Melillo and colleagues found had activity against HIF-1α, and also topoisomerase I. This group is exemplified by the compound NSC-609699 (topotecan Rapisarda et al. 2002). Topotecan does not affect HIF-1α protein accumulation, but inhibits its translation. He also presented data that indicates that Topoisomerase 1 is required for the inhibition of HIF-1α protein accumulation by topotecan camptothecin-resistant cell lines with known Topo 1 alterations do not exhibit HIF-1α inhibition when treated with topotecan (Rapisarda et al. 2004). He also showed that topotecan possessed anti-tumor activity against transplanted tumors in immunodeficient mice. A clinical trial is being planned to test the hypothesis that HIF-1 inhibition in tumors will result in increased tumor control and survival.

Amato Giaccia stated that, whereas the effect of loss of HIF-1α in tumors leads to inhibition of tumor growth, it does not eliminate tumors. Studies indicate that inhibition of HIF-1 leads to a tumor growth delay, but that in some tumors, growth can eventually resume in a HIF-1-independent manner. Therefore, it would be therapeutically more beneficial to eliminate cells with elevated HIF than to inhibit their growth (Sutphin et al. 2004). Thus, a HIF-directed cytotoxin could be found that would kill cells when HIF activity is elevated, such as by hypoxia, oncogenes, or growth-factor dysregulation. He reported on the isolation of a drug that kills cells deficient in VHL preferentially and that possess elevated HIF-1 activity. He stated the importance for a large high-throughput screen to find different families of such drugs to test in preclinical models for efficacy.

Mark Dewhirst (Duke University) presented the paradox of HIF-1 signaling during tumor reoxygenation/irradiation treatment. Last year, Garcia-Barros et al. published a paper that indicated that changing the intrinsic radiation sensitivity of the tumor vasculature resulted in increased regression of tumors treated with radiotherapy (Garcia-Barros et al. 2003). Previous studies have suggested a correlation between HIF-1 and an outcome in patients treated with radiotherapy (Aebersold et al. 2001) that could be explained by the fact that increased levels of HIF represented increased tumor hypoxia or dysregulated growth-factor expression. Mark Dewhirst presented data indicating that radiation-treated tumors induce HIF-1, which results in increased VEGF and bFGF that can act as survival factors for endothelial cells (Moeller et al. 2004). Surprisingly, it is radiation-induced reoxygenation of tumors that results in reactive oxygen species that induces HIF-1. Whether these reactive oxygen species differ from those generated by the mitochondria still needs to be determined, as well as their mechanisms of action. Do they increase HIF accumulation through a prolyl hydroxylase inhibition or through another mechanism? He also demonstrated the potential translation of these studies to the clinic by pretreating mice with the free radical scavenger AEOL-10113, which blocks the induction of HIF-1 activity, or YC-1, which is a small-molecule inhibitor of HIF-1, before irradiating them. Treatment with either compound that inhibits HIF resulted in increased tumor growth delay. In vitro reoxygenation of tumor cells results in a rapid decay in HIF-1 protein, suggesting that there is something unique about the reoxygenation of tumor cells that results in an increase in HIF and HIF target genes. A recent study by Mekhail may lend some insight into the fact that this increased level of HIF after reoxygenation occurs in regions of the tumor that are at low pH and result in decreased VHL activity (Mekhail et al. 2004). Thus, these studies suggest that HIF inhibitors would have a dual role in the tumor, in that they inhibit tumor cell growth and increase the sensitivity of endothelial cells to radiotherapy by inhibiting the production of endothelial cells survival factors. It will be important to determine the efficacy of this approach in human tumors. In contrast to treating solid tumors with an intact VHL and HIF pathway, the treatment of patients with pVHL-deficient tumors, such as those found in renal cell carcinoma, is prime for the concept of targeted therapy. Bill Kaelin stated that drugs that inhibit VEGF or its receptor have shown activity in clinical trials against renal cell carcinoma (Rini et al. 2004). As HIF-2 is sufficient and necessary for tumor growth and expansion of pVHL-deficient tumors, then the combination of HIF inhibitors to increase endothelial sensitivity and radiotherapy may have now some efficacy, where it previously had none.

Xulosa

Hypoxia-inducible responses are highly regulated in normal embryonic development and are dysregulated in a number of disease states, including cancer. The identification of oxygen-regulated proteins, such as the HIF family transcription factors, serves as a paradigm for oxygen sensing at the molecular level, but probably represents only one example on a much larger theme of protein regulation in response to hypoxia. A variety of intracellular organelles have also been implicated in oxygen sensing, such as ion channels, mitochondria, and the endoplasmic reticulum, and it will be important to clearly delineate whether they sense in changes in oxygen tension directly or through as yet unknown mechanisms. The use of model organisms, including transgenic and knockout mice, has been very instructive in linking molecular events in oxygen sensing with developmental responses, and should provide a more complete framework to understand what aspects of oxygen sensing are conserved during evolution. Finally, whereas the role of hypoxia and hypoxia-induced gene expression in malignant progression and response to therapy is supported by numerous studies, the question of the contributions of hypoxic tumor stroma and secretion of cytokines and chemokines to malignant progression is poorly understood and requires further study. The fundamental knowledge of how cells sense and respond to hypoxia has provided an important framework to understand the role of hypoxia in disease and cancer. The goal is that we can ultimately exploit this knowledge for diagnosis and treatment.