title: Time-resolved single-turnover of caa(3) oxidase from Thermus thermophilus. Fifth electron of the fully reduced enzyme converts O(H) into E(H) state.
abstract: The oxidative part of the catalytic cycle of the caa(3)-type cytochrome c oxidase from Thermus thermophilus was followed by time-resolved optical spectroscopy. Rate constants, chemical nature and the spectral properties of the catalytic cycle intermediates (Compounds A, P, F) reproduce generally the features typical for the aa(3)-type oxidases with some distinctive peculiarities caused by the presence of an additional 5-th redox-center-a heme center of the covalently bound cytochrome c. Compound A was formed with significantly smaller yield compared to aa(3) oxidases in general and to ba(3) oxidase from the same organism. Two electrons, equilibrated between three input redox-centers: heme a, Cu(A) and heme c are transferred in a single transition to the binuclear center during reduction of the compound F, converting the binuclear center through the highly reactive O(H) state into the final product of the reaction-E(H) (one-electron reduced) state of the catalytic site. In contrast to previous works on the caa(3)-type enzymes, we concluded that the finally produced E(H) state of caa(3) oxidase is characterized by the localization of the fifth electron in the binuclear center, similar to the O(H)→E(H) transition of the aa(3)-type oxidases. So, the fully-reduced caa(3) oxidase is competent in rapid electron transfer from the input redox-centers into the catalytic heme-copper site.
authors: Department of Molecular Energetics of Microorganisms, A.N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Russian Federation.
authors: Sergey A
authors: SA
authors: Siletsky
authors: Ilya
authors: I
authors: Belevich
authors: Nikolai P
authors: NP
authors: Belevich
authors: Tewfik
authors: T
authors: Soulimane
authors: Michael I
authors: MI
authors: Verkhovsky