7-Methylpterin and 7-methyllumizine: oxidative degradation products of 7-methyl-substituted pteridines in methanogenic bacteria.

7-Methylpterin and 7-methyllumizine were isolated and identified in extracts of methanogenic bacteria which had been extracted in air with ethanol-water. Ethanol-water preparations of cells extracted under nitrogen or hydrogen were devoid of these compounds. Extracts of cells obtained in the presence of air also had an increased amount of a complex arylamine which, on acid hydrolysis, gave 1 mol each of phosphate, 5-(p-aminophenyl)-1,2,3,4-tetrahydroxypentane, and alpha-hydroxyglutaric acid. Gas chromatography-mass spectrometry was used to identify the 5-(p-aminophenyl)-1,2,3,4-tetrahydroxypentane as its tetratrimethylsilyl derivative and the alpha-hydroxyglutaric acid as the n-butyl ester derivative of its gamma-lactone. When exposed to air, extracts of cells prepared in the absence of air produced 6-acetyl-7-methylpterin and 7-methylxanthopterin in addition to 7-methylpterin and 7-methyllumizine. It is concluded that these compounds are derived from the oxidative cleavage of the tetrahydromethanopterin, which is present in these bacteria, by a series of reactions analogous to those known to occur in the oxidative cleavage of tetrahydrofolic acid.