Zhao X J, Sampath V, Caughey W S
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins 80523, USA.
Biochem Biophys Res Commun. 1995 Jul 26;212(3):1054-60. doi: 10.1006/bbrc.1995.2076.
Reduction of nitric oxide (NO) to nitrous oxide (N2O) is catalyzed by bovine heart cytochrome c oxidase (CcO) in anaerobic solutions at pH 7.2 and 20 degrees C. Cyanide inhibits and forms Fea3(3+)CN. The mononitrosyl (Fea3(2+)NO), but not the dinitrosyl (Fea3(2+)NO; CuB+NO), is a likely intermediate in N2O formation. One-electron reduction of NO at Fea3(2+) could yield N2O via HNO. However, a two-electron reduction of the NO ligand to give an intermediate that reacts with a second NO to give N2O and H2O appears more likely. Conversion of NO to N2O is favored by low levels of both NO and O2, higher NO levels can inhibit both cytochrome c oxidase and NO reductase activities. Raising the O2 level will favor catalysis of NO oxidation to NO2 by CcO. The reactions of NO and the specific CcO activity that occur in tissue will be critically dependent on NO, O2, and CcO levels.
在pH 7.2和20摄氏度的厌氧溶液中，牛心细胞色素c氧化酶（CcO）可催化一氧化氮（NO）还原为一氧化二氮（N2O）。氰化物会抑制该反应并形成Fea3(3+)CN。单亚硝酰基（Fea3(2+)NO）而非双亚硝酰基（Fea3(2+)NO; CuB+NO）可能是N2O形成过程中的中间体。在Fea3(2+)处对NO进行单电子还原可能通过HNO生成N2O。然而，将NO配体进行双电子还原以产生一种中间体，该中间体再与第二个NO反应生成N2O和H2O似乎更有可能。低水平的NO和O2有利于NO转化为N2O，较高的NO水平会抑制细胞色素c氧化酶和NO还原酶的活性。提高O2水平将有利于CcO催化NO氧化为NO2。组织中发生的NO反应和特定的CcO活性将严重依赖于NO、O2和CcO的水平。
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