Methanopterin biosynthesis: methylation of the biosynthetic intermediates.

The basic scheme for the biosynthesis of methanopterin (MPT) in Methanobacterium thermoautotrophicum strain DeltaH, and M. thermoautotrophicum strain Marburg, has been shown to be the same as that recently determined for Methanosarcina thermophila strain TM-1. This scheme has, as one of its unique steps, the condensation of 4-aminobenzoic acid with 5-phospho-alpha-d-ribosyl diphosphate (PRPP) to form 4-(beta-d-ribofuranosyl)aminobenzene 5'-phosphate (beta-RFA-P). Labeling experiments with each of these organisms have established that the sites in the overall sequence of reactions from beta-RFA-P to MPT, where the S-adenosylmethionine-dependent C-9 and C-7 methylations of the pterin-containing intermediates occur, are organism related. In this work, cell extracts of M. thermoautotrophicum strain DeltaH, and M. thermoautotrophicum strain Marburg were found to contain significant amounts of methanopterin lacking the phosphate and 2-hydroxyglutaric acid groups.