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B6db references: 1920082

type Journal Article
authors Reynolds, K.; Martin, J.; Shen, S. J.; Esaki, N.; Soda, K.; Floss, H. G.
title Mechanistic studies of two amino acid racemases of broad substrate specificity from Pseudomonas striata and Aeromonas caviae
journal J Basic Microbiol
sel selected
ui 1920082
year (1991)
volume 31
number 3
pages 177-88
keywords Aeromonas/*enzymology
abstract The conversion of L-[alpha-2H]alanine in H2O and unlabeled L-alanine in 2H2O into D-alanine, under nearly irreversible conditions, with the amino acid racemase from Pseudomonas striata showed significant internal transfer of the alpha-hydrogen. This result has been interpreted as being indicative of a single base mechanism for the racemization. The relative rates of deuterium incorporation into unlabeled D- and L-methionine by the two amino acid racemases of broad substrate specificity from P. striata and Aeromonas caviae, were measured in 2H2O. The results showed a markedly different pattern, dependent upon the configuration of the initial substrate; with D- methionine as substrate deuterium is incorporated into both enantiomers at approximately the same rate, but with L-methionine as substrate deuterium is incorporated considerably faster into the D than the L enantiomer. These results argue against a single base mechanism of racemization for these enzymes and are best rationalized in terms of a double base model where only one of the bases undergoes proton (deuterium) exchange with the solvent while the amino acid is enzyme- bound. The interpretation of the earlier experiment needs to be considered in light of these results.
last changed 2009/07/02 14:11

B6db references