The role of formylmethanofuran: tetrahydromethanopterin formyltransferase in methanogenesis from carbon dioxide.

Formylmethanofuran: tetrahydromethanopterin formyltransferase was purified to electrophoretic homogeneity from cells of Methanobacterium thermoautotrophicum. The enzyme is a tetramer of similar or identical subunits (Mr = 41,000). The equilibrium favors transfer of the formyl group to tetrahydromethanopterin (H4MPT) at physiological pH. The product of formyl transfer by the purified enzyme was shown by a number of criteria to be 5-formyl-H4MPT, as opposed to 10-formyl-H4MPT or 5,10-methenyl-H4MPT. Reconstitution of a portion of the methanogenic C1 cycle was effected by combining purified formyltransferase, methenyl-H4MPT cyclohydrolase, formylmethanofuran, and H4MPT to give methenyl-H4MPT. Additional reconstitution experiments established that the formyltransferase is an essential enzyme for the conversion of carbon dioxide to methane. In conjunction with previously published data (Donnelly, M.I., Escalante-Semerena, J.C., Rinehart, K. L., Jr., and Wolfe, R.S. (1985) Arch. Biochem. Biophys. 242, 430-439), these data substantiate the role of 5-formyl-H4MPT as an intermediate of methanogenesis.