Biochemistry and Molecular Biology of Methane Monooxygenase

Methane oxidizing bacteria (methanotrophs) are a unique group of aerobic bacteria that can gain all of their carbon and energy requirements from methane. The enzymes that catalyze the first step in the bacterial methane oxidation pathway, the oxidation of methane to methanol, are called methane monooxygenases. These are remarkable enzymes because methane is chemically very stable and to convert methane to methanol chemically requires expensive catalysts, high temperatures and pressures. There are two types of methane monooxygenase that occur in methanotrophs, a membrane-bound, particulate methane monooxygenase and a cytoplasmic, soluble methane monooxygenase which belongs to a class of enzymes known as soluble di-iron monooxygenases. The expression of these enzymes in methanotrophs is often regulated by the availability of copper. The soluble methane monooxygenase has attracted significant attention and has considerable potential in biocatalysis and bioremediation since it can co-oxidize a very wide range of aliphatic and aromatic compounds, even though methanotrophs themselves do not grow on these compounds. We review here the biochemistry and molecular biology of both the particulate and soluble methane monooxygenases and their biotechnological potential.