Hooper A B, Debey P, Andersson K K, Balny C
Eur J Biochem. 1983 Jul 15;134(1):83-7. doi: 10.1111/j.1432-1033.1983.tb07534.x.
Hydroxylamine oxidoreductase (HAO) of Nitrosomonas catalyzes the dehydrogenation of NH2OH and subsequent addition of oxygen to form nitrite. HAO contains c hemes and the CO-binding heme P460 in a 7:1 ratio; dehydrogenation of NH2OH involves passage of electrons to P460 and then c hemes. We now report that electrons rapidly pass from c hemes of HAO to the P460 center and then to H2O2. This conclusion is supported by (a) inhibition of c heme oxidation with CO and (b) loss of H2O2-oxidizability of ferrous c hemes following specific destruction of heme P460. Reaction of ferrous P460 with H2O2 is rate-limiting. Activation of dioxygen for N-oxidation by ferrous HAO may involve the two-electron reduction of O2 by P460. The reaction of ferrous HAO with H2O2 was studied as it may reveal aspects of the mechanism of activation of dioxygen. Reaction of ferrous heme P460 with CO is slow and with low affinity as compared with other hemoproteins. Values for reaction of CO with enzyme were: k1, 1.1 X 10(-3) M-1 s-1 and Kd, 12 microM.
亚硝化单胞菌的羟胺氧化还原酶（HAO）催化NH2OH的脱氢反应以及随后的加氧反应以形成亚硝酸盐。HAO含有细胞色素c和CO结合型细胞色素P460，其比例为7:1；NH2OH的脱氢反应涉及电子传递至P460，然后再传递至细胞色素c。我们现在报道，电子迅速从HAO的细胞色素c传递至P460中心，然后再传递至H2O2。这一结论得到以下两点的支持：（a）CO对细胞色素c氧化的抑制作用；（b）在细胞色素P460被特异性破坏后，亚铁细胞色素c的H2O2氧化能力丧失。亚铁P460与H2O2的反应是限速反应。亚铁HAO对N-氧化的双氧激活可能涉及P460对O2的双电子还原。研究了亚铁HAO与H2O2的反应，因为它可能揭示双氧激活机制的某些方面。与其他血红素蛋白相比，亚铁细胞色素P460与CO的反应缓慢且亲和力低。CO与该酶反应的值为：k1，1.1×10(-3) M-1 s-1，Kd，12 μM。
