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.
Published Version
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