Oxidation of Hydrocarbons by Methane Monooxygenases from a Variety of Microbes

Methane monooxygenase is the enzyme responsible for the initial oxygenation of methane to methanol. The methanotrophs (methane-oxidizing bacteria) are divided into two types depending on whether they assimilate carbon via the ribulose monophosphate pathway (RMP) (type I) or serine pathway (type II), or both. The range of substrates oxidized and products observed from M. capsulatus and M. trichosporium extracts imply that the monooxygenases from these two organisms essentially are similar. The monooxygenase from M. methanica does not oxidize n-alkanes with more than six carbon atoms, or alicyclic, heterocyclic, and aromatic compounds. Experiments have shown that the extracts of M. methanica would catalyze the O2 and NADPH-dependent disappearance of bromomethane. They presented evidence that the methane monooxygenase was responsible for the catalysis by showing that the enzyme was particulate and stable to freezing but unstable at 2°C.