Structure and Biochemistry of Methane Monooxygenase Enzyme Systems

Methanotrophic bacteria play an important role in global methane cycling, metabolizing most of the methane produced by methanogenic bacteria before it reaches the atmosphere (Higgins et al., 1980) where it is a greenhouse gas (Chappellaz et al., 1990). In the first step of the metabolic pathway of these organisms (Figure 1), methane is oxidized to methanol by methane monooxgyenase enzyme systems (Anthony, 1982). These systems are mixed function oxidases, with one atom of dioxygen being incorporated into methanol and the other into water. Methanol is then further oxidized to formaldehyde which is assimilated into cellular biomass by one of several possible pathways, depending on the type of organism (Davies and Whittenbury, 1970; Hanson et al., 1991). Excess formaldehyde is converted to formate and to carbon dioxide.