title: Thiazolidine-2-carboxylic acid, an adduct of cysteamine and glyoxylate, as a substrate for D-amino acid oxidase.
abstract: A mixture of cysteamine and glyoxylate, proposed by Hamilton et al. to form the physiological substrate of hog kidney D-amino acid oxidase (Hamilton, G. A., Buckthal, D. J., Mortensen, R. M., and Zerby, K. W. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 2625-2629), was confirmed to act as a good substrate for the pure enzyme. As proposed by those workers, it was shown that the actual substrate is thiazolidine-2-carboxylic acid, formed from cysteamine and glyoxylate with a second order rate constant of 84 min-1 M-1 at 37 degrees C, pH 7.5. Steady state kinetic analyses reveal that thiazolidine-2-carboxylic acid is a better substrate at pH 8.5 than at pH 7.5. At both pH values, the catalytic turnover number is similar to that obtained with D-proline. D-Amino acid oxidase is rapidly reduced by thiazolidine-2-carboxylic acid to form a reduced enzyme-imino acid complex, as is typical with D-amino acid oxidase substrates. The product of oxidation was shown by NMR to be delta 2-thiazoline-2-carboxylic acid. Racemic thiazolidine-2-carboxylic acid is completely oxidized by the enzyme. The directly measured rate of isomerization of L-thiazolidine-2-carboxylic acid to the D-isomer was compared to the rate of oxidation of the L-isomer by D-amino acid oxidase. Their identity over the range of temperature from 2-30 degrees C established that the apparent activity with the L-amino acid can be explained quantitatively by the rapid, prior isomerization to D-thiazolidine-2-carboxylic acid.
mesh_terms: D000603:Amino Acids, Sulfur; D000818:Animals; D003543:Cysteamine; D003605:D-Amino-Acid Oxidase / Q000378:metabolism*; D006038:Glyoxylates; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D011392:Proline / Q000031:analogs & derivatives*; D013379:Substrate Specificity; D013552:Swine; D053778:Thiazolidines
chemical_list: D000603:Amino Acids, Sulfur; D006038:Glyoxylates; D053778:Thiazolidines; C021760:thiazolidine-2-carboxylic acid; D003543:Cysteamine; D011392:Proline; D003605:D-Amino-Acid Oxidase; C031150:glyoxylic acid