Activation of the hydroxylase of sMMO from Methylococcus capsulatus (Bath) by hydrogen peroxide

Hydrogen peroxide can activate the non-heme binuclear iron-containing hydroxylase of soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath) in the catalysis of oxidation of methane and other sMMO substrates. The reductase, protein B, O2 and NADH are normally required for catalytic activity, but can be replaced by H2O2 serving as the source of both oxygen and electrons for the reaction. Similar results have been observed in a different strain of MMO from Methylosinus trichosporium OB3b (Andersson, K.K., Froland, W.A., Lee, S.-K. and Lipscomb, J.D. (1991) New J. Chem. 15, 410-415). The Km,app for H2O2 was found to be 66 mM. Labelled oxygen experiments show that the oxygen atom in the product in the peroxide driven system is derived from H2O2 and not O2. Using C2-C5 alkanes and 2-butene as substrates it was shown that the product distribution differed in the complete sMMO and H2O2-driven systems, indicating that more than one pathway is available to the enzyme. Protein B, which is required for catalytic activity in the complete system, was found to be an inhibitor of the hydroxylase/H2O2 system. It was also observed that protein B not only affected the activity, but also the selectivity of carbon hydroxylation with 2-methylbutane as substrate.