Mechanistic studies of two amino acid racemases of broad substrate specificity from Pseudomonas striata and Aeromonas caviae
✍ Scribed by Kevin Reynolds; Jennifer Martin; Shu-Jane Shen; Nobuyoshi Esaki; Kenji Soda; Prof. Dr. Heinz G. Floss
- Book ID
- 102910355
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- English
- Weight
- 830 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0233-111X
No coin nor oath required. For personal study only.
✦ Synopsis
The conversion of ~-[a-~H]alanine in H 2 0 and unlabeled L-alanine in 'H,O into D-alanine, under nearly irreversible conditions, with the amino acid racemase from Pseudomonas striata showed significant internal transfer of the cc-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 cauiue, were measured in ' H 2 0 . The results showed a markedly different pattern, dependent upon the configuration of the initial substrate; with D-methionhe 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.