Titration and steady-state behaviour of the 830 nm chromophore in cytochrome c oxidase.
Titration and steady-state behaviour of the 830 nm chromophore in cytochrome c oxidase.
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细胞色素 c 氧化酶中 830 nm 发色团的滴定和稳态行为。
DOI：
10.1042/bj2030541
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发表时间：
1982
期刊：
影响因子：
--
通讯作者：
G. Chanady
中科院分区：
文献类型：
--
作者：
P. Nicholls;G. Chanady
氰化物培养的细胞色素c氧化酶（牛心脏细胞色素aa3）与铁细胞色素c或NNN' n '-四甲基-对苯二胺滴定，最初每mol细胞色素aa3有两个还原当量。第一个等价物降低细胞色素血红素铁；第二个还原当量与还原830 nm发色团（e.p.r可检测的铜）无关，但可能需要还原e.p.r不可检测的铜。过量的还原剂在细胞色素aa3的氰化物络合物中引入第三个还原物。在细胞色素c和抗坏血酸存在的稳态呼吸过程中，830 nm的发色团几乎完全被氧化。在厌氧条件下，它的还原速度比细胞色素a慢。在甲酸盐或叠氮化物的存在下，在830 nm处出现了一定的还原；在氧脉冲系统中，细胞色素c和a的稳态还原减少与830nm物质的ab还原增加有关。在甲酸抑制体系中，厌氧反应中a3的还原呈现一个滞后期，其持续时间与830 nm物种的还原时间相对应。结果表明，在反应过程中，e.p.r -不可检出铜（CuD）的还原时间较早，而可检出铜（CuD）的还原时间较晚。后一种可能负责细胞色素a3血红素的减少。无法检测到的铜和a3血红素之间的磁性关联可能并不意味着电子转移的能力，而电子转移更容易发生在细胞色素a3和830nm的物质之间。
Titration of cyanide-incubated cytochrome c oxidase (ox heart cytochrome aa3) with ferrocytochrome c or with NNN'N'-tetramethyl-p-phenylenediamine initially introduces two reducing equivalents per mol of cytochrome aa3. The first equivalent reduces the cytochrome a haem iron; the second reducing equivalent is not associated with reduction of the 830 nm chromophores (e.p.r.-detectable copper) but is probably required for reduction of the e.p.r.-undetectable copper. Excess reductant introduces a third reducing equivalent into the cyanide complex of cytochrome aa3. During steady-state respiration in the presence of cytochrome c and ascorbate, the 830 nm chromophore is almost completely oxidized. It is reduced more slowly than cytochrome a on anaerobiosis. In the presence of formate or azide, some reduction at 830 nm can be seen in the steady state; in an oxygen-pulsed system, a decrease in steady-state reduction of cytochromes c and a is associated with ab increased reduction of the 830 nm species. In the formate-inhibited system the reduction of a3 on anaerobiosis shows a lag phase, the duration of which corresponds to the time taken for the 830 nm species to be reduced. It is concluded that the e.p.r.-undetectable copper (CuD) is reduced early in the reaction sequence, whereas the detectable copper (CUD) is reduced late. The latter species is probably that responsible for reduction of the cytochrome a3 haem. The magnetic association between undetectable copper and the a3 haem may not imply capability for electron transfer, which occurs more readily between cytochrome a3 and the 830 nm species.