REGIOSELECTIVITY AND STEREOSELECTIVITY OF PARTICULATE METHANE MONOOXYGENASE FROM METHYLOCOCCUS-CAPSULATUS (BATH)

The regiospecificity and stereoselectivity of alkane hydroxylation and alkene epoxidation by the particulate methane monooxygenase from Meth ylococcus capsulatus (Bath) was evaluated over a range of substrates. Oxidation products were identified by conventional GC analysis, and th e stereoselectivity of oxidation was determined by a combination of ch iral GC and HPLC methods, as well as H-1 NMR analysis of the correspon ding (R)-2-acetoxy-2-phenylethanoate ester derivatives in the case of alkanol products. Alkane hydroxylation was found to proceed favoring a ttack at the C-2 position in all cases, and the stereoselectivity for n-butane and n-pentane was characterized by an enantiomeric excess of 46% and 80%, respectively, with preference for the (R)-alcohol noted f or both substrates. Epoxides were formed with smaller stereoselectivit ies. Together, the regio-and stereoselectivity results suggest that an equilibrium of competing substrate binding modes exists. A simple sub strate-binding model that incorporates preferential C-2 oxidation with the observed stereoselectivity of alkane hydroxylation is proposed, a nd hypotheses for the general mechanism are suggested and discussed.