Methanol Biosynthesis Using Methanotrophs
Selective oxidation of methane to methanol under ambient conditions is desired for the usage of methane. Biological conversion of methane to methanol by methanotrophs is one of the most useful methods for methane conversion. Therefore, many researchers have studied about methane monooxygenase structure, active site, and mechanism of the oxidation of methane to methanol. This review summarizes our studies on the biological methanol synthesis and the characterization of methane monooxygenase that catalyzes methane to methanol conversion in methanotrophs. In methanol biosynthesis using methanotrophs, the inhibition of methanol dehydrogenase by cyclopropanol and the reversible inhibition of methane monooxygenase by methanol are described. To increase methanol biosynthesis, semicontinuous reactor was designed. To further improve biosynthesis, purification and characterization of methane monooxygenase were carried out. Electron paramagnetic resonance studies revealed that particulate methane monooxygenase has copper ions as metal centers and the instability of purified particulate methane monooxygenase is partially due to the intrinsic formation of hydrogen peroxide. As electron donor for the methane oxidation is important for biosynthesis, the construction of the photoinduced hydroxylation of methane using water as an electron donor was examined.