INVIVO C-13 AND N-15 NMR-STUDIES OF METHYLAMINE METABOLISM IN PSEUDOMONAS SPECIES MA

Pseudomonas species MA was grown with methylamine as a sole source of carbon and nitrogen enabling the total flow of carbon and nitrogen into this organism to be simultaneously monitored in vivo using C-13 and N-15 NMR. [C-13]Methylamine was rapidly and extensively incorporated into the methyl group of N-methylglutamate during high oxygenation of the cell suspension, but when the oxygenation rate was lower, a significant portion was also found in the methyl group of gamma-glutamylmethylamide. At later times the carbon label was found in intermediates of the serine assimilation pathway, with glutamate derived from the tricarboxylic acid cycle being the most abundant product. Incorporation of [N-15]methylamine was only detected as N-methyl[N-15]glutamate, but when protein synthesis was inhibited, the label was also detected in the amino nitrogen of glutamate. When oxygenation rates were lower, the N-15-labeled methylamine was found in the methylamide group of gamma-glutamylmethylamide in addition to being incorporated into N-methylglutamate. Gamma-glutamylmethylamide formation was linked to the overall energy state of the cell and was not affected by inhibition of the carbon assimilation pathway. Neither 5-hydroxy-N-methylpyroglutamate nor N-methyl-alpha-ketoglutaramate were detected to any significant extent. A mechanism was proposed for the role of gamma-glutamylmethylamide in the regulation of endogenous nitrogen supplies in this organism.