Electron transfer reactions in the soluble methane monooxygenase of Methylococcus capsulatus (Bath)

Abstract

Aerobic stopped‐flow experiments have confirmed that component C is the methane monooxygenase component responsible for interaction with NADH. Reduction of component C by NADH is not the rate‐limiting step for component C in the methane monooxygenase reaction. Removal and reconstitution of the redox centres of component C suggests a correlation between the presence of the FAD and Fe2S2 redox centres and NADH: acceptor reductase activity and methane monooxygenase activity respectively, consistent with the order of electron flow: NADH → FAD → Fe2S2→ component A. This order suggests that component C functions as a 2e−1/1e−1 transformase, splitting electron pairs from NADH for transfer to component A via the one‐electron‐carrying Fe2S2 centre. Electron transfer has been demonstrated between the reductase component, component C and the oxygenase component, component A, of the methane monooxygenase complex from Methylococcus capsulatus (Bath) by three separate methods. This intermolecular electron transfer step is not rate‐determining for the methane monooxygenase reaction. Intermolecular electron transfer was independent of component B, the third component of the methane monooxygenase. Component B is required to switch the oxidase activity of component A to methane monooxygenase activity, suggesting that the role of component B is to couple substrate oxidation to electron transfer, via the methane monooxygenase components. Copyright © 1985, Wiley Blackwell. All rights reserved