Nicholls P, Kim J K
Can J Biochem. 1982 Jun;60(6):613-23. doi: 10.1139/o82-076.
Anomalies both kinetic and equilibrium in nature are described for the inhibition of cytochrome c oxidase activity by sulphide in the isolated enzyme and in submitochondrial particles. These anomalies are related to the involvement of more than 1 mol of sulphide in the blockage of one cytochrome aa3 centre. Sulphide reduces resting cytochrome a3, a reaction that results in oxygen uptake and the loss of a sulphide molecule. Sulphide can also reduce cytochromes c and a; in the former case, a part of the one-equivalent oxidation product, presumed to be the SH radical, reacts with oxygen. Such oxygen uptake is also seen under aerobic conditions when ferricyanide reacts with sulphide. Three phases are identified in the inhibitory interaction of sulphide with the cytochrome c oxidase enzyme itself: an initial rapid reaction involving sulphide oxidation, oxygen uptake, and conversion of cytochrome aa3 into the low-spin "oxyferri" form; a subsequent step in which sulphide reduces cytochrome a; and the final inhibitory step in which a third molecule of sulphide binds the a3 iron centre in the cytochrome a2+ a3 3+ (oxy) species to give cytochrome a2+ a3 3+ H2S. the initial events parallel some of the events in the interaction of the cytochrome c-cytochrome aa3 system with monothiols; the final inhibitory event resembles that with cyanide.
在分离的酶和亚线粒体颗粒中，描述了硫化物对细胞色素c氧化酶活性抑制的动力学和平衡异常。这些异常与超过1摩尔硫化物参与阻断一个细胞色素aa3中心有关。硫化物还原静止的细胞色素a3，该反应导致氧气摄取和一个硫化物分子的损失。硫化物还可以还原细胞色素c和a；在前一种情况下，假定为SH自由基的一价氧化产物的一部分与氧气反应。当铁氰化物与硫化物反应时，在有氧条件下也会观察到这种氧气摄取。在硫化物与细胞色素c氧化酶本身的抑制相互作用中确定了三个阶段：初始快速反应，涉及硫化物氧化、氧气摄取以及细胞色素aa3转化为低自旋“氧铁”形式；随后一步是硫化物还原细胞色素a；最后一个抑制步骤是第三个硫化物分子与细胞色素a2+a33+(氧)物种中的a3铁中心结合，生成细胞色素a2+a33+H2S。初始事件与细胞色素c-细胞色素aa3系统与单硫醇相互作用中的一些事件相似；最后的抑制事件类似于与氰化物的相互作用。
