Carbon dioxide reduction factor and methanopterin, two coenzymes required for CO2 reduction to methane by extracts of Methanobacterium.

Carbon dioxide reduction (CDR) factor is contained in a low molecular weight fraction of cell extract that is required for methane production from CO2 by resolved cell extracts. This fraction has been separated into two components both of which have been highly purified. One component is methanopterin, and for the other component the name CDR factor is retained. No known coenzymes tested substitute in the methane-producing assay for CDR factor and methanopterin, both of which are stable to boiling and exposure to air. The ultraviolet-visible spectrum of CDR factor has a peak at 273 nm, a shoulder at 280 nm, and at pH 1, a peak at 219 nm. The ultraviolet-visible spectrum of methanopterin isolated from the CDR fraction is similar to the spectrum previously reported for this compound (Keltjens, J. T., and Vogels, G. D. (1981) in Microbial Growth on C1 Compounds (Dalton, H., ed) pp. 152-158, Heyden and Son, Ltd., London). The addition of CDR factor (0.8 micrograms) and methanopterin (50 micrograms) to the assay mixture increased by 12-fold the amount of methane formed from CO2.