Proton-coupled electron transfer at the Qo site:: what type of mechanism can account for the high activation barrier?

被引:66
作者
Crofts, AR
Guergova-Kuras, M
Kuras, R
Ugulava, N
Li, JY
Hong, SJ
机构
[1] Univ Illinois, Dept Biochem, Roger Adams Lab 419, Urbana, IL 61801 USA
[2] Univ Illinois, Ctr Biophys & Computat Biol, Urbana, IL 61801 USA
来源
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS | 2000年 / 1459卷 / 2-3期
关键词
myxothiazol; stigmatellin; activation energy; mutagenesis; proton-coupled electron transfer;
D O I
10.1016/S0005-2728(00)00184-5
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
In Rhodobacter sphaeroides, transfer of the first electron in quinol oxidation by the bc(1) complex shows kinetic features (a slow rate (approx. 1.5X10(3)/s), high activation energy (approx. 65 kJ/mol) and reorganization energy, lambda (2.5 V)) that are unexpected from Marcus theory and the distances shown by the structures. Reduction of the oxidized iron-sulfur protein occurs after formation of the enzyme-substrate complex, and involves a I-I-transfer in which the electron transfer occurs through the approx. 7 Angstrom of a bridging histidine forming a H-bond with quinol and a ligand to 2Fe-2S, The anomalous kinetic features can be explained by a mechanism in which the electron transfer is constrained by coupled transfer of the proton. We discuss this in the context of mutant strains with modified E-m.7 and pK for the iron-sulfur protein, and Marcus theory for proton-coupled electron transfer. We suggest that transfer of the second proton and electron involve movement of semiquinone in the Q(o) site, and rotation of the Glu of the conserved -PEWY- sequence. Mutational studies show a key role for the domain proximal to heme b(L). The effects df mutation at Tyr-302 (Tyr-279 in bovine sequence) point to a possible linkage between conformational changes in the proximal domain, and changes leading to closure of the iron-sulfur protein access channel at the distal domain. (C) 2000 Elsevier Science B.V. All rights reserved.
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页码:456 / 466
页数:11
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