Exploring the proton pump mechanism of cytochrome c oxidase in real time
2007
Belevich, Ilya | Bloch, Dmitry A. | Belevich, Nikolai | Wikström, Mårten | Verkhovsky, Michael I.
Cytochrome c oxidase catalyzes most of the biological oxygen consumption on Earth, a process responsible for energy supply in aerobic organisms. This remarkable membrane-bound enzyme also converts free energy from O₂ reduction to an electrochemical proton gradient by functioning as a redox-linked proton pump. Although the structures of several oxidases are known, the molecular mechanism of redox-linked proton translocation has remained elusive. Here, correlated internal electron and proton transfer reactions were tracked in real time by spectroscopic and electrometric techniques after laser-activated electron injection into the oxidized enzyme. The observed kinetics establish the long-sought reaction sequence of the proton pump mechanism and describe some of its thermodynamic properties. The 10-μs electron transfer to heme a raises the pKa of a "pump site," which is loaded by a proton from the inside of the membrane in 150 μs. This loading increases the redox potentials of both hemes a and a₃, which allows electron equilibration between them at the same rate. Then, in 0.8 ms, another proton is transferred from the inside to the heme a₃/CuB center, and the electron is transferred to CuB. Finally, in 2.6 ms, the preloaded proton is released from the pump site to the opposite side of the membrane.
اظهر المزيد [+] اقل [-]الكلمات المفتاحية الخاصة بالمكنز الزراعي (أجروفوك)
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