Rousseau D L, Ching Y, Wang J
AT&T Bell Laboratories, Murray Hill, New Jersey 07974.
J Bioenerg Biomembr. 1993 Apr;25(2):165-76. doi: 10.1007/BF00762858.
An analysis of resonance Raman scattering data from CO-bound cytochrome c oxidase and from the photodissociated enzyme indicates that histidine may not be coordinated to the iron atom of cytochrome a3 in the CO-bound form of the enzyme. Instead, the data suggest that either a water molecule or a different amino acid residue occupies the proximal ligand position. From these data, it is postulated that ligand exchange on cytochrome a3 can occur under physiological conditions. Studies of mutant hemoglobins have demonstrated that tyrosinate binds preferentially to histidine in the ferric forms of the proteins. In cytochrome c oxidase tyrosine residues are located near the histidine residues recently implicated in coordination to cytochrome a3 (Shapleigh et al., 1992; Hosler et al., this volume). Expanding on these concepts, we propose a model for proton translocation at the O2-binding site based on proximal ligand exchange between tyrosine and histidine on cytochrome a3. The pumping steps take place at the level of the peroxy intermediate and at the level of the ferryl intermediate in the catalytic cycle and are thereby consistent with the recent results of Wilkstrom (1989) who found that proton pumping occurs only at these two steps. It is shown that the model may be readily extended to account for the pumping of two protons at each of the steps.
对一氧化碳结合型细胞色素c氧化酶和光解离酶的共振拉曼散射数据的分析表明，在该酶的一氧化碳结合形式中，组氨酸可能未与细胞色素a3的铁原子配位。相反，数据表明水分子或其他氨基酸残基占据了近端配体位置。根据这些数据推测，细胞色素a3上的配体交换可能在生理条件下发生。对突变血红蛋白的研究表明，在蛋白质的铁离子形式中，酪氨酸根优先与组氨酸结合。在细胞色素c氧化酶中，酪氨酸残基位于最近与细胞色素a3配位有关的组氨酸残基附近（沙普利等人，1992年；霍斯勒等人，本卷）。基于这些概念的拓展，我们提出了一个在氧气结合位点质子转运的模型，该模型基于细胞色素a3上酪氨酸和组氨酸之间的近端配体交换。泵送步骤发生在催化循环中的过氧中间体水平和高铁中间体水平，因此与威尔克斯特伦（1989年）最近的结果一致，他发现质子泵送仅发生在这两个步骤。结果表明，该模型可以很容易地扩展以解释每个步骤中两个质子的泵送。
