A team of UK researchers has helped uncover the mystery of exactly how soil bacteria catalyse the reduction of nitrous oxide.
A team of UK researchers has helped uncover the mystery of exactly how soil bacteria catalyse the reduction of nitrous oxide, N2O, to nitrogen gas.
N2O is an important greenhouse gas which contributes to global warming. Experiments designed to understand how it is released into the atmosphere have gathered pace in recent years.
N2O reduction is the final stage in the denitrification process that converts soluble nitrate ions derived from artificial fertilisers into N2. An enzyme found in soil bacteria called nitrous oxide reductase (N2OR) catalyses the reduction of N2O to N2. The active site of N2OR is a copper-sulfide cluster that forms a complex with N2O. During the reduction process, electrons from one enzyme molecule transfer to a copper-N2O complex on another.
N2O reduction starts when one of the enzyme sites is fed electrons from an outside donor, in this case a molecule called cytochrome c (Cyt c).
A team of investigators, led by Andrew Thomson at the University of East Anglia, measured the rates of electron transfer between Cyt c and the active site of N2OR to help understand the precise reduction mechanism.
Thomson discovered that the transfer of electrons from Cyt c to the enzyme pair takes place only after a short time lag.
The time delay can be explained by a small but important structural change that happens when Cyt c approaches the enzyme pair. Without this structural change, electron transfer is not possible and the reduction of N2O slows dramatically.
The model is still hypothetical, but Thomson thinks it might help solve the riddle of why N2OR reduces N2O in such a controlled manner.
Watafiti wa Uingereza wamegundua jinsi bakteria za udongo zinavyoweza kupunguza oksidi ya nitrous. Watafiti wa Uingereza wamegundua jinsi bakteria za udongo zinavyoweza kuharibu oksidi ya nitrous kuwa gesi ya nitrojeni. N2O ni gesi muhimu ya chafu ambayo inachangia ongezeko la joto duniani. Majaribio ya kuelewa jinsi inavyoachiliwa katika angahewa yameongezeka sana katika miaka ya karibuni. N2O ni hatua ya mwisho katika mchakato wa denitrification ambayo hubadilisha ions nitrate soluble inayotokana na mbolea bandia katika N2. Enzyme inayoitwa nitrous oxide reductase (NOR) hutengeneza N2O. N2O-C2O ni kundi la sulfidi ya shaba ambayo huunda nyenzo ngumu na N2O. Katika mchakato wa kupunguzwa, elektroni kutoka molekuli moja ya enzyme hupitishwa kwa nyenzo ya shaba-N2O kwenye nyingine. N2O kupunguzwa huanza wakati moja ya maeneo ya enzyme ni kulishwa elektroni kutoka mtoaji nje, katika kesi hii molekuli aitwaye cytochrome c. Timu ya watafiti iliyoongozwa na Andrew Thomson katika Chuo Kikuu cha East Anglia, ilipima viwango vya uhamisho wa elektroni kati ya CytC na tovuti ya N2O, kusaidia kuelewa utaratibu sahihi wa kupunguzwa. Thomson aligundua kwamba uhamisho wa elektroni kutoka Cyt c kwa jozi ya enzyme hufanyika tu baada ya kuchelewesha kwa muda mfupi. Ucheleweshaji wa wakati unaweza kuelezwa na mabadiliko madogo lakini muhimu ya muundo ambayo hutokea wakati Cyt c inakaribia jozi ya enzyme. Bila mabadiliko haya ya muundo, uhamisho wa elektroni hauwezekani na kupunguzwa kwa N2O hupungua sana. "Tumekuwa tukifanya utafiti wa kina, lakini Thomson anasema kwamba ""tunaweza kugundua ni kwa nini N2O hupungua kwa njia inayoweza kudhibitiwa."""