De Vries S, Albracht S P, Berden J A, Slater E C
Biochim Biophys Acta. 1982 Jul 22;681(1):41-53. doi: 10.1016/0005-2728(82)90276-6.
The kinetic behaviour of the prosthetic groups and the semiquinones in in QH2:cytochrome c oxidoreductase has been studied using a combination of the freeze-quench technique, low-temperature diffuse-reflectance spectroscopy, EPR and stopped flow. (2) In the absence of antimycin, cytochrome b-562 is reduced in two phases separated by a lag time. The initial very rapid reduction phase, that coincides with the formation of the antimycin-sensitive Qin, is ascribed to high-potential cytochrome b-562 and the slow phase to low-potential cytochrome b-562. the two cytochromes are present in a 1:1 molar ratio. The lag time between the two reduction phases decreases with increasing pH. Both the [2 Fe-2S] clusters and cytochrome c1 are reduced monophasically under these conditions, but at a rate lower than that of the initial rapid reduction of cytochrome b-562. (3) In the presence of antimycin and absence of oxidant, cytochrome b-562 is still reduced biphasically, but there is no lag between the two phases. No Qin is formed and both the Fe-S clusters and cytochrome c1 are reduced biphasically, one-half being reduced at the same rate as in the absence of antimycin and the other half 10-times slower. (4) In the presence of antimycin and oxidant, the recently described antimycin-insensitive species of semiquinone anion, Qout (De Vries, S., Albracht, S.P.J., Berden, J.A. and Slater, E.C. (1982) J. Biol. Chem. 256, 11996-11998) is formed at the same rate as that of the reduction of all species of cytochrome b. In this case cytochrome b is reduced in a single phase. (5) The reversible change of the line shape of the EPR spectrum of the [2Fe-2S] cluster 1 is caused by ubiquinone bound in the vicinity of this cluster. (6) The experimental results are consistent with the basic principles of the Q cycle. Because of the multiplicity, stoicheiometry and heterogeneous kinetics of the prosthetic groups, a Q cycle model describing the pathway of electrons through a dimeric QH2:cytochrome c oxidoreductase is proposed.
利用冷冻淬灭技术、低温漫反射光谱、电子顺磁共振和停流技术相结合的方法，研究了QH2：细胞色素c氧化还原酶中辅基和半醌的动力学行为。（2）在没有抗霉素的情况下，细胞色素b-562分两个阶段还原，中间有一个延迟时间。最初非常快速的还原阶段与抗霉素敏感的Q in的形成同时发生，归因于高电位细胞色素b-562，而缓慢阶段归因于低电位细胞色素b-562。这两种细胞色素以1:1的摩尔比存在。两个还原阶段之间的延迟时间随着pH值的升高而缩短。在这些条件下，[2Fe-2S]簇和细胞色素c1均单相还原，但速率低于细胞色素b-562最初快速还原的速率。（3）在存在抗霉素且不存在氧化剂的情况下，细胞色素b-562仍然双相还原，但两个阶段之间没有延迟。没有形成Q in，Fe-S簇和细胞色素c1均双相还原，其中一半以与没有抗霉素时相同的速率还原，另一半慢10倍。（4）在存在抗霉素和氧化剂的情况下，最近描述的抗霉素不敏感的半醌阴离子物种Q out（De Vries，S.，Albracht，S.P.J.，Berden，J.A.和Slater，E.C.（1）982）J. Biol. Chem. 256，11996 - 11998）的形成速率与所有细胞色素b物种的还原速率相同。在这种情况下，细胞色素b单相还原。（5）[2Fe-2S]簇1的电子顺磁共振谱线形状的可逆变化是由结合在该簇附近的泛醌引起的。（6）实验结果与Q循环的基本原理一致。由于辅基的多样性、化学计量和异质动力学，提出了一个描述电子通过二聚体QH2：细胞色素c氧化还原酶途径的Q循环模型。
