Studies on partially reduced mammalian cytochrome oxidase reactions with ferrocytochrome c.
Studies on partially reduced mammalian cytochrome oxidase reactions with ferrocytochrome c.
复制标题
部分还原哺乳动物细胞色素氧化酶与铁细胞色素 c 反应的研究。
DOI：
10.1042/bj1570591
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
T. Brittain
中科院分区：
文献类型：
--
作者：
C. Greenwood;T. Brittain
通过停流和温度跳跃的快速分光光度技术研究了铁细胞色素c和部分还原的哺乳动物细胞色素氧化酶之间发生的电子转移过程的动力学。停流实验显示在 605 nm 和 563 nm 处初始非常快的消光变化，表明细胞色素 a 的同时还原和铁细胞色素 c 的氧化。在这个“爆发”阶段，例如混合后的前 50 毫秒，总是发现被氧化的细胞色素 c 多于被还原的细胞色素 a。这种电子当量的差异可能是由于酶中另一个氧化还原位点的快速减少造成的，这可能与在 830 nm 处观察到的消光变化有关。在制备部分还原氧化酶的培养期间，在恒定的反应物浓度下，铁细胞色素c还原细胞色素a的速率随时间降低。温跃实验表明存在两个弛豫过程。两个阶段中较快的一个被指定为细胞色素 c 和细胞色素 a 之间的电子转移反应。对这一相的弛豫时间倒数浓度依赖性的研究得出，从细胞色素 c 到细胞色素 a 的电子转移速率常数为 9 X 10(6)M-1-s-1，逆反应的速率常数为 8.5 X 10(6)M-1-s-1。因此，电子转移反应的平衡常数接近于1。较慢的阶段被解释为细胞色素 a 和氧化酶分子内另一个氧化还原位点之间电子转移的信号。
The kinetics of the electron-transfer process which occurs between ferrocytochrome c and partially reduced mammalian cytochrome oxidase were studied by the rapid spectrophotometric techniques of stopped flow and temperature jump. Stopped-flow experiments showed initial very fast extinction changes at 605 nm and at 563 nm, indicating the simultaneous reduction of cytochrome a and oxidation of ferrocytochrome c. During this 'burst' phase, say the first 50 ms after mixing, it was invariably found that more cytochrome c had been oxidized than cytochrome a had been reduced. This discrepancy in electron equivalents may be accounted for by the rapid reduction of another redox site in the enzyme, possibly that associated with the extinction changes observed at 830 nm. During the incubation period in which the partially reduced oxidase was prepared, the rate of reduction of cytochrome a by ferrocytochrome c, at constant reactant concentrations, decreased with time. Temperature-jump experiments showed the presence of two relaxation processes. The faster of the two phases was assigned to the electron-transfer reaction between cytochrome c and cytochrome a. A study of the concentration-dependence of the reciprocal relaxation time for this phase yielded a rate constant of 9 X 10(6)M-1-s-1 for the electron transfer from cytochrome c to cytochrome a, and a value of 8.5 X 10(6)M-1-s-1 for the reverse reaction. The equilibrium constant for the electron-transfer reaction is therefore close to unity. The slower phase has been interpreted as signalling the transfer of electrons between cytochrome a and another redox site within the oxidase molecule.