Chromatium flavocytochrome c: kinetics of reduction of the heme subunit, and the flavocytochrome c-mitochondrial cytochrome c complex.
Chromatium flavocytochrome c: kinetics of reduction of the heme subunit, and the flavocytochrome c-mitochondrial cytochrome c complex.
复制标题
Chromatium flavocytochrome c：血红素亚基还原动力学，以及 flavocytochrome c-线粒体细胞色素 c 复合物。
DOI：
10.1016/0003-9861(85)90605-8
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发表时间：
1985
影响因子：
3.9
通讯作者：
Cusanovich,MA
中科院分区：
文献类型：
--
作者：
Meyer,TE;Vorkink,WP;Tollin,G;Cusanovich,MA
研究了激光闪光光解产生的外源黄素中性半醌还原葡萄色菌黄素细胞色素酶亚基的动力学。与全蛋白不同，分离的血红素亚基与光黄素中性半醌反应明显。测得的反应速率常数（2.7 × 107 m − 1 s −1）与具有类似氧化还原电位的c型细胞色素相当。与FMN中性自由基反应的离子强度依赖性表明血红素亚基在还原位点具有小的负电荷。两者合计，这些结果表明，血红素亚基的活性位点被埋在与黄素亚基在holoprotein络合。马细胞色素与铬离子形成强络合物，而与绿离子、黄细胞色素不形成强络合物。可能的生理电子受体如HiPIP、cytochromec′和cytochromec-555显然不与flavocytochromesc结合。马细胞色素与黄细胞色素复合物被光黄素自由基还原的速率常数约为马细胞色素酮还原的速率常数的两倍。黄色素本身不与外源性黄素半醌类反应。FMN自由基还原复合物的离子强度依赖性也小于马细胞色素在flavocytochromec的情况下。亚硫酸盐与蛋白质结合的FAD（FAD以8-α-S-半胱氨酸键结合）形成加合物，不影响马细胞色素蛋白与黄细胞色素蛋白复合物的还原。我们得出结论，马cytochromecis直接减少外源性黄素在其复杂的flavocytochromec，虽然动力学略有修改。这些结果与线粒体细胞色素与细胞色素氧化酶或细胞色素b 5复合物的观察结果并无不同。
The kinetics of reduction ofChromatium vinosumflavocytochromecheme subunit by exogenous flavin neutral semiquinones generated by laser flash photolysis have been investigated. Unlike the holoprotein, the isolated heme subunit was appreciably reactive with lumiflavin neutral semiquinone. The measured rate constant for the reaction (2.7 × 107m−1s−1) was comparable to those ofc-type cytochromes having similar redox potentials. The ionic strength dependence of the reaction with FMN neutral radical indicated that the heme subunit had a small negative charge at the site of reduction. Taken together, these results suggest that the active site of the heme subunit is buried on complexation with the flavin subunit in the holoprotein. Horse cytochromecformed a strong complex withChromatium, but notChlorobium, flavocytochromec. Possible physiological electron acceptors such as HiPIP, cytochromec′, and cytochromec-555 apparently did not bind to the flavocytochromesc. The rate constant for reduction by lumiflavin radical of horse cytochromeccomplexed to flavocytochromecwas about twofold smaller than for reduction of horse cytochromecalone. Flavocytochromecwas itself unreactive with exogenous flavin semiquinones. The ionic strength dependence of the reduction of the complex by FMN radical was also smaller than for horse cytochromecin the absence of flavocytochromec. Sulfite, which forms an adduct with the protein-bound FAD (FAD is bound in an 8-α-S-cysteinyl linkage), did not affect the reduction of horse cytochromecin its complex with flavocytochromec. We conclude that horse cytochromecis reduced directly by exogenous flavins in its complex with flavocytochromec, although the kinetics are slightly modified. These results are not unlike observations made with complexes of mitochondrial cytochromecwith cytochrome oxidase or cytochromeb5.