A study of the metabolism of L-alpha gamma-diaminobutyric acid in a Xanthomonas species.

1. l-alphagamma-Diaminobutyric acid is metabolized in Xanthomonas sp. to aspartic beta-semialdehyde, aspartic acid and oxaloacetic acid. 2. Aspartic beta-semialdehyde is formed from diaminobutyric acid by a pyruvate-dependent gamma-transamination. 3. The transaminase has a pH optimum of 9 and exhibits a high degree of substrate specificity, as analogues of diaminobutyric acid and pyruvate are inert in the system. The transaminase is inhibited by carbonyl-binding agents such as hydroxylamine. 4. Aspartic acid is formed from aspartic beta-semialdehyde by an NAD(+)-dependent dehydrogenation. 5. The dehydrogenase has a pH optimum of 8.5 and is a thiol enzyme. It is specific for aspartic beta-semialdehyde but analogues of NAD(+) such as 3-acetylpyridine-adenine dinucleotide and deamino-NAD are partly active in the system. 6. The significance of these reactions is discussed in relation to diaminobutyric acid metabolism in plants and mammalian systems.