Methane Hydroxylation with Water as an Electron Donor under Light Irradiation in the Presence of Reconstituted Membranes Containing both Photosystem II and a Methane Monooxygenase.

Methane/methanol conversion is one of the most important chemical reactions. Methane monooxygenases from methanotrophs are enzymes that catalyze methane/methanol conversion under mild conditions. Here we report the reconstitution of purified photosystem II (PSII) from Thermosynechococcus elongatus BP-1 into the membrane fraction containing particulate methane monooxygenase (pMMO) from Methylosinus trichosporium OB3b. Photoinduced hydroxylation of methane to methanol was successfully achieved by using the PSII-reconstituted membrane containing pMMO under light irradiation. This result indicates that the sequential redox chain from PSII through the quinone pool to pMMO can be constructed and that water can serve as the electron donor for methane hydroxylation under irradiation with light. pMMO in the membrane fraction produced hydrogen peroxide as a byproduct when an electron donor was added for methane hydroxylation, whereas under light irradiation conditions the PSII-reconstituted membrane containing pMMO did not generate hydrogen peroxide. Optimization of the electron-transfer rate can easily be achieved with this system by tuning the light intensity.