Oxygenated cytochrome o (Vitreoscilla) formed by treating oxidized cytochrome with superoxide anion

概要

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Oxygenated cytochrome o can be formed experimentally in two ways, i) by reaction of reduced cytochrome o with molecular oxygen, or ii) by reaction of oxidized cytochrome o with superoxide anion generated by the action of the xanthine oxidase system. It is thermodynamically feasible for oxidized cytochrome o plus O_2^-, and reduced cytochrome o plus O_2 to appear as intermediates in reactions i) and ii), respectively. Superoxide dismutase completely inhibits the xanthine oxidase-catalyzed con-version of oxidized cytochrome o into the oxygenated form but it has relatively little effect on the oxygenated cytochrome o formation in the reaction system consisting of NADH, NADH-cytochrome o reductase, and cytochrome o. Thus, if superoxide anion does play a significant role in the latter system it must be efficiently coupled to react with cytochrome o and inaccessible to superoxide dismutase. Direct electron transfer from the reductase to the cytochrome without the involvement of superoxide anion is an alternative mechanism.
日本植物生理学会の論文