Laser flash photolysis studies of electron transfer mechanisms in cytochromes: an aromatic residue at position 82 is not required for cytochrome c reduction by flavin semiquinones or electron transfer from cytochrome c to cytochrome oxidase.
Laser flash photolysis studies of electron transfer mechanisms in cytochromes: an aromatic residue at position 82 is not required for cytochrome c reduction by flavin semiquinones or electron transfer from cytochrome c to cytochrome oxidase.
复制标题
细胞色素中电子转移机制的激光闪光光解研究：黄素半醌还原细胞色素 c 或从细胞色素 c 到细胞色素氧化酶的电子转移不需要 82 位的芳香族残基。
DOI：
10.1016/0003-9861(92)90098-h
复制
发表时间：
1992
影响因子：
3.9
通讯作者：
Tollin,G
中科院分区：
文献类型：
--
作者：
Hazzard,JT;Mauk,AG;Tollin,G
用激光闪光光解方法研究了酵母iso-1-细胞色素c第82位的芳香族侧链对其电子转移反应动力学的影响，比较了一系列定点突变细胞色素被游离黄素半喹酮还原和从还原的细胞色素向牛细胞色素c氧化酶的电子转移。虽然一些突变体(S82、Y82、I82)与野生型(F82)或G82细胞色素在被鲁米黄素半喹酮还原的二级速率常数上有很小的差异(约10%)，但这些差异与侧链芳香性无关。在铁细胞色素与细胞色素c氧化酶的反应中，82位含有脂肪残基的突变株对指数的偏离明显大于野生型或Y82突变株。我们根据细胞色素在氧化酶结合位点内的多个取向来解释非指数行为；这种情况发生的程度显然受到第82位残基的性质的影响。然而，对不同突变体的电子转移到细胞色素氧化酶的平均速率常数的比较表明，除了I82明显较慢(约三倍)外，所有突变体都与WT非常相似。这些结果，结合以前从稳态动力学和热力学测量获得的结果，表明所观察到的突变体之间的差异是由于细胞色素与氧化酶结合方式的改变，而不是由于对第82位存在芳香基团的特定要求。
The influence of an aromatic side chain at position 82 of yeast iso-1-cytochrome c on the kinetics of its electron transfer reactions has been investigated using laser flash photolysis methods to compare a series of site-specific mutant cytochromes in their reduction by free flavin semiquinone and in electron transfer from reduced cytochrome to bovine cytochrome c oxidase. Although small (approximately 10%) but significant differences are observed between some of the mutants (S82, Y82, I82) and wild-type (F82) or G82 cytochrome in the second-order rate constant for reduction by lumiflavin semiquinone, these do not correlate with side-chain aromaticity. In the reaction between the ferrocytochromes and cytochrome c oxidase, significantly larger deviations from exponentiality are found for those mutants having aliphatic residues at position 82 than for wild type or Y82. We interpret the nonexponential behavior in terms of multiple orientations of the cytochromes within the oxidase binding site; the extent to which this occurs is apparently influenced by the character of the residue at position 82. However, a comparison of the average rate constants for electron transfer to cytochrome oxidase for the various mutants reveals that all are closely comparable to WT, except for I82 which is significantly slower (approximately threefold). These results, combined with those obtained previously from steady-state kinetic and thermodynamic measurements, suggest that the observed differences among the mutants are due to alterations in the mode of binding of the cytochrome to the oxidase, rather than to a specific requirement for the presence of an aromatic group at position 82.