心脏细胞色素c1和细胞色素c的复合物

Chiang Y L, Kaminsky L S, King T E

J Biol Chem. 1976 Jan 10;251(1):29-36.

The interactions of cytochrome c1 and cytochrome c from bovine cardiac mitochondria were investigated. Cytochrome c1 and cytochrome c formed a 1:1 molecular complex in aqueous solutions of low ionic strength. The complex was stable to Sephadex G-75 chromatography. The formation and stability of the complex were independent of the oxidation state of the cytochrome components as far as those reactions studied were concerned. The complex was dissociated in solutions of ionic strength higher than 0.07 or pH exceeding 10 and only partially dissociated in 8 M urea. No complexation occurred when cytochrome c was acetylated on 64% of its lysine residues or photooxidized on its 2 methionine residues. Complexes with molecular ratios of less than 1:1 (i.e. more cytochrome c) were obtained when polymerized cytochrome c, or cytochrome c with all lysine residues guanidinated, or a "1-65 heme peptide" from cyanogen bromide cleavage of cytochrome c was used. These results were interpreted to imply that the complex was predominantly maintained by ionic interactions probably involving some of the lysine residues of cytochrome c but with major stabilization dependent on the native conformations of both cytochromes. The reduced complex was autooxidizable with biphasic kinetics with first order rate constants of 6 X 10(-5) and 5 X U0(-5) s-1 but did not react with carbon monoxide. The complex reacted with cyanide and was reduced by ascorbate at about 32% and 40% respectively, of the rates of reaction with cytochrome c alone. The complex was less photoreducible than cytochrome c1 alone. The complex exhibited remarkably different circular dichroic behavior from that of the summation of cytochrome c1 plus cytochrome c. We concluded that when cytochromes c1 and c interacted they underwent dramatic conformational changes resulting in weakening of their heme crevices. All results available would indicate that in the complex cytochrome c1 was bound at the entrance to the heme crevice of cytochrome c on the methionine-80 side of the heme crevice.

对来自牛心脏线粒体的细胞色素c1和细胞色素c之间的相互作用进行了研究。在低离子强度的水溶液中，细胞色素c1和细胞色素c形成了1:1的分子复合物。该复合物对葡聚糖凝胶G - 75层析稳定。就所研究的那些反应而言，复合物的形成和稳定性与细胞色素组分的氧化态无关。该复合物在离子强度高于0.07的溶液中或pH超过10时会解离，在8M尿素中仅部分解离。当细胞色素c的64%的赖氨酸残基被乙酰化或其2个甲硫氨酸残基被光氧化时，不发生络合。当使用聚合的细胞色素c、或所有赖氨酸残基都被胍基化的细胞色素c、或细胞色素c经溴化氰裂解得到的“1 - 65血红素肽”时，可得到分子比小于1:1（即更多细胞色素c）的复合物。这些结果被解释为意味着该复合物主要通过离子相互作用维持，可能涉及细胞色素c的一些赖氨酸残基，但主要的稳定性取决于两种细胞色素的天然构象。还原后的复合物具有双相动力学的自动氧化能力，一级速率常数分别为6×10⁻⁵和5×10⁻⁵ s⁻¹，但不与一氧化碳反应。该复合物与氰化物反应，并分别以约单独与细胞色素c反应速率的32%和40%被抗坏血酸还原。该复合物的光还原能力比单独的细胞色素c1弱。该复合物表现出与细胞色素c1加细胞色素c总和显著不同的圆二色性。我们得出结论，当细胞色素c1和c相互作用时，它们会发生剧烈的构象变化，导致其血红素裂隙变弱。所有现有结果表明，在复合物中，细胞色素c1结合在细胞色素c血红素裂隙蛋氨酸 - 80一侧的血红素裂隙入口处。