Pearce L L, Pitt B R, Peterson J
Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
J Biol Chem. 1999 Dec 10;274(50):35763-7. doi: 10.1074/jbc.274.50.35763.
Fully and partially reduced forms of isolated bovine cytochrome c oxidase undergo a two-electron oxidation-reduction process with added peroxynitrite, leading to catalytic oxidation of ferrocytochrome c to ferricytochrome c. The other major reaction product is nitrite ion, 86% of the added peroxynitrite being measurably converted to this species. The reaction is inhibited in the presence of cyanide, implicating the heme a(3)-Cu(B) binuclear pair as the active site. Moreover, provided peroxynitrite is not added to excess, the reductase activity of the enzyme toward this oxidant efficiently protects other protein and detergent molecules in vitro from nitration of tyrosine residues and oxidative damage. If the enzyme is exposed to approximately 10(2)-fold excesses of peroxynitrite, then significant irreversible loss of electron transfer activity results, and the heme a(3)-Cu(B) binuclear pair no longer undergo a characteristic carbon monoxide-driven reduction. The accompanying rather small changes in the observed electronic absorption spectrum are suggestive of a modification in the vicinity of one or both hemes but probably not to the cofactors themselves.
分离的牛细胞色素c氧化酶的完全还原形式和部分还原形式与添加的过氧亚硝酸根发生双电子氧化还原过程，导致亚铁细胞色素c催化氧化为高铁细胞色素c。另一个主要反应产物是亚硝酸根离子，添加的过氧亚硝酸根中有86%可测量地转化为该物种。该反应在氰化物存在下受到抑制，这表明血红素a(3)-铜(B)双核对是活性位点。此外，只要不过量添加过氧亚硝酸根，该酶对这种氧化剂的还原酶活性就能在体外有效地保护其他蛋白质和去污剂分子免受酪氨酸残基的硝化和氧化损伤。如果该酶暴露于约100倍过量的过氧亚硝酸根中，那么电子传递活性就会出现显著的不可逆损失，并且血红素a(3)-铜(B)双核对不再经历特征性的一氧化碳驱动的还原。观察到的电子吸收光谱伴随的相当小的变化表明一个或两个血红素附近发生了修饰，但可能不是辅因子本身。
