Purification and characterisation of D-amino acid aminotransferase from Rhizobium japonicum.
Rhizobium japonicum has D-amino acid aminotransferase and alanine racemase activities. The D-amino-acid aminotransferase has been partially purified and characterized. This enzyme has a broad specificity and is very active with D-alpha-aminobutyrate and D-aspartate as well as D-alanine and D-glutamate. The stereospecificity of the enzyme for D-amino acids was apparently absolute with respect to product inhibition, pyridoxamine formation as well as catalytic activity. The apparent molecular weight was 58,000 and the pH optimum was 7.8-7.9. The equilibrium constant in the direction of D-glutamate formation was 1.9. Initial-velocity kinetic studies indicate the enzyme acts by a ping-pong mechanism. The dissociation constant for pyridoxal phosphate and the Michaelis constants (+/- standard errors) for D-alanine and 2-oxoglutarate were determined to be 0.51 +/- 0.06 micrometer, and 2.13 +/- 0.18 and 0.058 +/- 0.005 mM respectively. The enzyme is moderately inhibited (30%) by 4 mM p-chloromercuribenzoate.
D000410:Alanine Transaminase / Q000378:metabolism; D000596:Amino Acids; D001219:Aspartate Aminotransferases / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D012231:Rhizobium / Q000201:enzymology*; D013053:Spectrophotometry; D013237:Stereoisomerism; D013379:Substrate Specificity; D000637:Transaminases / Q000302:isolation & purification / Q000378:metabolism*
D000596:Amino Acids; D000637:Transaminases; D001219:Aspartate Aminotransferases; D000410:Alanine Transaminase