Biosynthesis of the 7-methylated pterin of methanopterin.

The incorporation of [15N]glycine and [U-methyl-2H]methionine into methanopterin by growing cells of a methanogenic bacterium was measured to establish the biosynthetic route of the methylated pterin in the structure. The tetrahydromethanopterin produced by the cells was oxidatively cleaved to produce 7-methylpterin, and the amount of label incorporated into this pterin was measured by gas chromatography-mass spectrometry of the ditrimethylsilyl derivative of this compound. Approximately 27% of the 7-methylpterin and the guanine present in the cell was derived from the fed [15N]glycine. [U-methyl-2H]methionine was incorporated with the initial retention of all three deuteriums. These results are consistent with the biosynthesis of the pterin of methanopterin originating from GTP and its 7-methyl group arising from the methyl group of methionine.