Methane monooxygenase (MMO) catalyzes the most difiinilt alkane oxida tion reaction, conversion of methane to methanol. and the oxidations t.f many other hydrocarbons as well. The mechanism of C-H oxidation by MMO ha been extensively studied, but romains controversial. In this .udy. the rea< t ion of methylcubane with the reconstituted MMO system tmin M. frtrfio.iponuni was investigated. As a radical clock substrate, methylcubane rearranges rapidly (lU]Us') following radical generation on the methyl group. It wa re ported that the reaction of this s übst rate with MMO from M. capxulnttis gave only methyl hydroxylation product. 1 he lack ol cube opening and cubyl by droxylation products were taken a& indications of A concerted oxygen insertion reaction for the. enzyme. In marked contrast. \ve observed that hydroxylation of the substrate by MMO from M. trn'hofiponuni occurred at both methyl and cubyl C-H positions. In addition, a major unknown product was found. Based on CîC and mass spectrornetry information, it was tentatively assigned as the rearranged, cube opened product for this radical clock, suggesting the forma tion of a radical intermediate in the reaction. The radical Hves about 10 -10s. as given by rough estimates of product abundance and knowledge of radical rearrangement rate. This result is consistent with our proposal th;it the reac tion proceeds through a hydrogen abstraction process, as indicated by previous experiments from our laboratory. Supported by MH Cirant CM KMtifi.
|Original language||English (US)|
|State||Published - Dec 1 1997|