The mechanism of methane and dioxygen activation in the catalytic cycle of methane monooxygenase.

The binuclear structure of the active center of methane monooxygenase plays a determining role in dioxygen activation and in selectivity and specificity of alkane oxidation with this enzyme. A new mechanism is suggested for binding and activation of O2, which involves side-on binding of O2-(2) to iron atoms followed by its conversion to the bis-mu-oxo complex considered as an alternative of ferryl in CH4 activation. This mechanism results in the sequence of the cleavage of the O-O bond of peroxide O/O2-instead of the opposite sequence O2-/O, which takes place in the case of heme monooxygenase cytochrome P-450. Therefore, in this case there is no necessity of the charge relay system [N.B. Gerber and S.G. Sligar, J. Am. Chem. Soc. 114 (1992) 8742] for the transformation of O2 to an active intermediate. The experiment for checking this hypothesis is suggested.