A novel one-carbon carrier (carboxy-5,6,7,8-tetrahydromethanopterin) isolated from Methanobacterium thermoautotrophicum and derived from methanopterin.

During short-term labeling experiments, cells of Methanobacterium thermoautotrophicum incorporated a substantial part of 14CO2 in a compound with a bright yellow fluorescence on dry thin-layer chromatography plates and called yellow fluorescent compound (YFC) [Daniels, L. and Zeikus, J.G. (1978) J. Bacteriol. 136, 75-84]. This compound was extracted and purified by ion-exchange column chromatography with formic acid gradients up to 0.3 M. Out of 325 g wet cells of M. thermoautotrophicum about 4 mg of the compound were isolated. This material and some degradation products obtained from it were studied by means of chemical decomposition, ultraviolet-visible-light spectroscopy and preliminary 1H-NMR spectroscopy. It has structural elements in common with methanopterin (see preceding paper in this journal); these elements are a pterin group, glutamate, a hexosamine. The pterin in this compound is present in a reduced form, presumably as 5,6,7,8-tetrahydromethanopterin, and the additional one-carbon unit is probably present as a carboxy group. Probably the first step of methanogenesis implies a carboxylation of methanopterin and a concomitant reduction of the pterin. The trivial name carboxy-5,6,7,8-tetrahydromethanopterin is introduced for the compound.