A Simple Colorimetrie Assay for Aspartate Aminotransferase

γ-Glutamylmethylamide (γ-GMA) synthetase was detected in crude extracts of Methylophaga sp. AA-30, but neither methylamine dehydrogenase nor N-methylglutamate dehydrogenase was observed. A large amount of γ-GMA was accumulated in the cells when the growth on methanol-methylamine was inhibited with iodoacetate, but the accumulation was not observed in the cells grown on methanol-(NH₄)₂SO₄. It is thought that γ-GMA is a metabolic intermediate of the methylamine-dissimilating pathway in the bacterium. In addition, γ-GMA-dissimilating enzymes were found in methylamine-grown cells. The enzymes, which consisted of H protein and L protein, required α-ketoglutaric acid, Mg²⁺ or Mn²⁺, and ammonia as a cofactor. Although the enzyme catalyzed the formation of glutamate from γ-GMA, it did not catalyze the formation of N-methylglutamate. Consequently, in this bacterium, methylamine seems to be metabolized through a different pathway from the N-methylglutamate pathway.