Biosynthesis of methanopterin

This paper establishes the pathway for the biosynthesis of methanopterin in Methanosarcina thermophila to proceed by the following series of reactions. First, 5-phospho-alpha-D-ribosyl diphosphate (PRPP) and 4-aminobenzoic acid condense together to produce 4-(beta-D-ribofuranosyl)aminobenzene 5'-phosphate, which then reacts with 6-hydroxymethyl-7,8-H(2)pterin pyrophosphate to produce 7,8-H(2)pterin-6-ylmethyl-4- (beta-D-ribofuranosyl) aminobenzene 5'-phosphate (3'). Compound 3' is then reduced to 7,8-H(2)pterin-6-ylmethyl- 1-(4-aminophenyl)-1-deoxy-D-ribitol 5'-phosphate (4') in a reaction stimulated by the addition of FMN or factor F-420 Dephosphorylation of compound 4' leads to 7,8-H(2)pterin-6-ylmethyl 1-(4-aminophenyl)-1-deoxy-D-ribitol (5'). Compound 5' then condenses with another molecule of PRPP to form 7, 8-H(2)pterin-6-ylmethyl-1-(4-aminophenyl)-1-deoxy-5-[1-alpha-D-ribofuranosyl 5-phosphate]-D-ribitol (9'). Compound 9', in the presence of ATP, then condenses with (S)-2-hydroxyglutaric acid to form demethylated H(2)methanopterin, a known precursor to methanopterin. The occurrence of this pathway was confirmed by (a) the chemical and/or biochemical synthesis of most of the proposed intermediates, (b) the detection of these intermediates in cell-free extracts, and (c) by the measurement of their conversion to demethylated methanopterin and/or other intermediates in the pathway.