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Journal of Biochemistry Advance Access originally published online on February 13, 2009
Journal of Biochemistry 2009 145(5):685-691; doi:10.1093/jb/mvp026
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© The Authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved

Intramolecular Electron Transfer Processes in CuB-deficient Cytochrome bo Studied by Pulse Radiolysis

Kazuo Kobayashi1, Seiichi Tagawa1 and Tatsushi Mogi2,3,*

1Institute of Scientific and Industrial Research, Osaka University, Mihogaoka, Ibaraki, Osaka 567-0047; 2ATP System Project, ERATO, JST, Nagatsuta 5800-2, Midori-ku, Yokohama 226-0026; and 3Department of Biomedical Chemistry, Graduate School of Medicine, the University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

*To whom correspondence should be addressed. Tel: +81 3 5841 8202, Fax: +81 3 5841 3444, E-mail: tmogi{at}m.u-tokyo.ac.jp.

Received December 25, 2008; Accepted February 6, 2009


  Abstract

The Escherichia coli cytochrome bo is a heme-copper terminal ubiquinol oxidase, and functions as a redox-driven proton pump. We applied pulse radiolysis technique for studying the one-electron reduction processes in the CuB-deficient mutant, His333Ala. We found that the CuB deficiency suppressed the heme b-to-heme o electron transfer two order of the magnitude (4.0x102 s–1), as found for the wild-type enzyme in the presence of 1 mM KCN (3.0x102 s–1). Potentiometric analysis of the His333Ala mutant revealed the 40 mV decrease in the Em value for low-spin heme b and the 160 mV increase in the Em value of high-spin heme o. Our results indicate that CuB not only serves as one-electron donor to the bound dioxygen upon the O-O bond cleavage, but also facilitates dioxygen reduction at the heme-copper binuclear centre by modulating the Em value of heme o through magnetic interactions. And the absence of a putative OH– bound to CuB seems not to affect the uptake of the first chemical proton via K-channel in the His333Ala mutant.

Key Words: copper B mutant, cytochrome bo, electron transfer, pulse radiolysis, quinol oxidase

Abbreviations: NMA, N-methylnicotinamide; QH, the high-affinity quinone-binding site; QL, the low-affinity quinol-oxidation site; Qn, ubiquinone-n; QnH2, ubiquinol-n; SML, sucrose monolaurate


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