HEMOGLOBIN NA IYA ZAMA MARAS HAƊIN KAI FIYE DA YADDA LITTATTAFAN KARATU SUKE FAƊA

Hemoglobin, furotin da ke ɗaukar oxygen a cikin jininmu, shi ne kuma misalin littattafan karatu na haɗin kai (cooperativity): da zarar ya kama ƙwayar oxygen ɗaya, yana kama na gaba cikin sauƙi, har zuwa huɗu. Wannan ne ke ba shi damar cika gaba ɗaya a cikin huhu ya kuma sauke su a cikin kyallen jiki (tissues). Samfura biyu na gargajiya suna bayyana shi — samfurin L. Pauling na 1935, inda gurabun kamawa huɗu ke taimakon juna, da samfurin Monod-Wyman-Changeux (MWC) na 1965, inda dukan ƙwayar ke sauyawa tsakanin siffofi biyu da ke riƙe oxygen da ƙarfi ko kuma a sassauƙa.

Dukkansu yawanci ana lissafa su a yanayi ɗaya: ƙwayar hemoglobin guda ɗaya da aka nutsar a cikin ma’ajiya (reservoir) ta ƙwayoyin oxygen masu ’yanci, wadda ake bayyanawa da matsi (pressure). Masana kimiyyar lissafi suna kiran wannan “grand canonical ensemble”. Lanƙwasar cikawa (saturation curve) — yawan oxygen da hemoglobin ke riƙe a kowane matsi — tana fitowa daga gare shi, kuma ana karanta haɗin kai daga wannan lanƙwasa.

Ma’ajiyar da babu ita

A. E. Allahverdyan da abokan aiki, a Alikhanyan National Laboratory da Yerevan State University a Armeniya, sun nuna cewa a cikin ƙwayar jan jini, wannan ma’ajiyar babu ita. Yawan (concentration) oxygen mai ’yanci da ya narke a cikin ƙwayar ya gaza na oxygen da ke manne da hemoglobin aƙalla sau 100 — kuma wannan ne ainihin dalilin samuwar hemoglobin. Akwai kusan ƙwayoyin hemoglobin 30 ga kowace ƙwayar oxygen mai ’yanci. Ko a cikin jinin arteries (arterial blood), yawancin ƙwayoyin hemoglobin ba su da oxygen mai ’yanci a ko’ina kusa da su: kowace ɗaya tana ganin ƙwayoyi huɗu da take riƙe da su kawai.

Don haka ƙungiyar ta bayyana yanayin ta wata hanya dabam: hemoglobin ɗaya da ƙwayoyin oxygen kaɗan — biyar a mafi yawa — a cikin juzu’i (volume) tsayayye, wato “canonical ensemble”. Wannan juzu’in ya dogara ne kan yadda aka matse hemoglobin a cikin ƙwayar: kusan ninki huɗu na juzu’in ƙwayar kanta, wani kubi (cube) mai tsawon gefe nanomita 6.93. A wannan hoton, oxygen yana shiga ko fita bisa bambance-bambancen free energy (makamashi mai ’yanci), ma’auni na wane tsari ne ƙididdiga (statistics) ta fi so.

(a) Sabon hoto: hemoglobin ɗaya (da’ira) tare da ƙwayoyin oxygen ɗinsa huɗu a cikin juzu’i kusan ninki huɗu na nasa. (b) Hoton da aka saba: hemoglobin a cikin ma’ajiyar ƙwayoyin oxygen masu ’yanci da yawa. (c) Hemoglobin biyu maƙwabta na iya musayar oxygen. — Hoto na 1, Allahverdyan da abokan aiki (2026), arXiv:2611.00824.

Haɗin kai mafi rauni

Ƙungiyar ta daidaita (fitted) samfuran gargajiya biyun da daidaitattun bayanai kan yadda hemoglobin ke sakin oxygen yayin da matsin oxygen ke sauka — ƙwaya ta farko tana fita tsakanin torr 80 da 40, ta ƙarshe tsakanin torr 20 da 7.5.

• A cikin samfurin Pauling, ma’aunin haɗin kai (1 na nufin babu shi) ya fito 1.88 a sabon tsarin, idan aka kwatanta da 6.32 a tsarin da aka saba, an daidaita su da bayanai iri ɗaya. Daidaitawar Pauling ta asali, da tsofaffin bayanai, ta ba da 12.
• A cikin samfurin MWC, rabo tsakanin ƙarfin son oxygen (oxygen affinities) na siffofin biyu — ma’auni na yadda ƙwayar ta kauce daga kamawa mai sauƙi, mai zaman kanta — ya fito kusan 4.7, idan aka kwatanta da 95.4 a tsarin da aka saba.

Har yanzu ana buƙatar ɗan haɗin kai. Ba tare da shi ba, hemoglobin zai iya cika a cikin huhu amma zai yi wa kyallen jiki da ke hutawa kawai hidima.

Matakan free energy na samfurin Pauling ga ƙwayoyin oxygen ɗaya zuwa huɗu da aka kama. Layukan kwance suna nuna tagogin aikin jiki (physiological windows); mafi kyawun daidaitawa kawai (baƙaƙen alwatika, haɗin kai 1.88) ne ya faɗa cikin dukkansu. Sauran launuka suna nuna haɗin kai mafi ƙarfi (magenta, ruwan ƙasa) da rashinsa (shuɗi). — Hoto na 2, Allahverdyan da abokan aiki (2026), arXiv:2611.00824.

Lokacin da haɗin kai ya zama zubewa a jere

A sabon tsarin ma, haɗin kai da ya yi yawa yana zama haɗari. Da ma’auni na 4.83, lissafin yana haifar da zubewa a jere (cascade): da zarar ƙwayar oxygen ta farko ta fita, sauran ukun suna fita kai tsaye — yanayin da marubutan suka kira wanda ba za a amince da shi ba, domin zai kai ga gubar oxygen. A 7.83, hemoglobin ba zai iya cika a cikin huhu kwata-kwata ba. Darajojin tsarin da aka saba, idan aka shigo da su cikin sabon, su ma suna haifar da rashin kwanciyar hankali (instabilities). Tsarin da aka saba kuwa, bai sanya irin waɗannan iyakoki ba.

Sabon hoton yana kuma sauya halin ƙwayar. A bayanin da aka saba, adadin ƙwayoyin oxygen da aka kama yana sauyawa (fluctuates) kusan daidai da matsakaicin darajarsa. A cikin canonical, da ƙyar yake sauyawa: hemoglobin yana yin kama da na’ura, yana ɗauka da sakin oxygen mataki-mataki, kuma ƙwayar da ta cika ba ta jawo ƙari.

Oxygen mai tsalle

Marubutan sun fitar da wani sakamako guda: tun da hemoglobin maƙwabta na iya musayar oxygen bisa free energy ɗinsu, oxygen zai iya tafiya a cikin ƙwayar jan jini, a wani ɓangare, ta hanyar tsalle daga wani hemoglobin zuwa na gaba. Gwada wannan ra’ayi zai buƙaci samfura masu motsi (dynamic models). Binciken na ka’ida ne (theoretical), kuma iyakokinsa na aikin jiki, a kalaman marubutan, “na al’ada ne zuwa wani mataki” (“somewhat conventional”) — amma yana tambayar wani ginshiƙi na yadda littattafan ilimin halitta ke bayyana oxygen da ke cikin jininmu.