Time-resolved O_H → E_H transition of the aberrant ba

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• 作者：Sergey A. Siletsky ; Ilya Belevich ; Må ; rten Wikströ ; m ; Tewfik Soulimane ; Michael I. Verkhovsky
• 关键词：Catalytic cycle ; Cytochrome c oxidase ; Electron transfer ; Thermus thermophilus ; Cytochrome ba₃
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2009
• 出版时间：March 2009
• 年：2009
• 卷：1787
• 期：3
• 页码：201-205
• 全文大小：454 K

文摘

The kinetics of single-electron injection into the oxidized nonrelaxed state (O_H → E_H transition) of the aberrant ba₃ cytochrome oxidase from Thermus thermophilus, noted for its lowered efficiency of proton pumping, was investigated by time-resolved optical spectroscopy. Two main phases of intraprotein electron transfer were resolved. The first component (τ  17 μs) reflects oxidation of Cu_A and reduction of the heme groups (low-spin heme b and high-spin heme a₃ in a ratio close to 50:50). The subsequent component (τ  420 μs) includes reoxidation of both hemes by Cu_B. This is in significant contrast to the O_H → E_H transition of the aa₃-type cytochrome oxidase from Paracoccus denitrificans, where the fastest phase is exclusively due to transient reduction of the low-spin heme a, without electron equilibration with the binuclear center. On the other hand, the one-electron reduction of the relaxed O state in ba₃ oxidase was similar to that in aa₃ oxidase and only included rapid electron transfer from Cu_A to the low-spin heme b. This indicates a functional difference between the relaxed O and the pulsed O_H forms also in the ba₃ oxidase from T. thermophilus.