Andréasson L E
Eur J Biochem. 1975 May 6;53(2):591-7. doi: 10.1111/j.1432-1033.1975.tb04102.x.
The reaction between cytochrome c oxidase and ferrocytochrome c has been investigated by the stopped-flow method. It has been found that only one electron acceptor, a heme group, in the oxidase is rapidly reduced by cytochrome c. The presence of N3- does not affect the reduction of the acceptor, which supports the hypothesis that this is identical with cytochrome a. The results are consistent with the existence of a simple equilibrium between cytochrome a and cytochrome c: c-2 + a-3+ in equilibrium c-3+ + a-2+ with an equilibrium constant corresponding to an oxidation-reduction potential of cytochrome a 30 mV higher than that for cytochrome c at pH 7.4. The oxidation-reduction potential of the a-3+ /a-2+ couple, 285 mV (based on a potential of 255 mV for cytochrome c), and the optical properties of the reduced form indicate that it is identical with neither of the reduced hemes seen in potentiometric titrations. The oxidase species resulting from the rapid reduction of cytochrome a by cytochrome c is proposed to represent a metastable intermediate state which, under anaerobic conditions, eventually is transformed into a more stable state characterized by a reduced high-potential heme.
采用停流法研究了细胞色素c氧化酶与亚铁细胞色素c之间的反应。已发现氧化酶中只有一个电子受体，即一个血红素基团，可被细胞色素c迅速还原。N3-的存在并不影响受体的还原，这支持了该受体与细胞色素a相同的假说。结果与细胞色素a和细胞色素c之间存在简单平衡相一致：c-2 + a-3+ 处于平衡状态 c-3+ + a-2+，其平衡常数对应的细胞色素a的氧化还原电位比pH 7.4时细胞色素c的氧化还原电位高30 mV。a-3+ /a-2+ 电对的氧化还原电位为285 mV（基于细胞色素c的电位为255 mV），还原形式的光学性质表明它与电位滴定中看到的两种还原血红素都不相同。细胞色素c使细胞色素a迅速还原产生的氧化酶物种被认为代表一种亚稳态中间体，在厌氧条件下，最终会转变为以还原的高电位血红素为特征的更稳定状态。
