The Replacement by Thiazolidinecarboxylic Acid of Exogenous Cystine and Cysteine

Publisher Website
Google Scholar
Abstract
The heterocyclic ring compound, L-thiazolidine-4-carboxylic acid, can replace dietary cystine (cysteine) for purposes of growth and protein synthesis. On the basis of its sulfur content, thiazolidinecarboxylic acid is as effective as cystine as a growth factor. Thiazolidinecarboxylic acid is even more active than cysteine as a detoxifying agent in the pulmonary edema produced by thiourea. However, thiazolidinecarboxylic acid, like cystine, is unable to replace completely either dietary methionine or homocystine. The ability of thiazolidinecarboxylic acid to substitute for cystine in the diet is eliminated by removing the carboxyl group or by inserting an extra methylene group in the ring. N-Formylcysteine, the mitochondrial oxidation product of thiazolidinecarboxylic acid, is as effective as its metabolic precursor in promoting growth on a cystine deficient diet. N,N′-Diformylcystine is also active in growth experiments. These experiments indicate that thiazolidinecarboxylic acid is converted quantitatively to cysteine and cystine, via N-formylcysteine, in the intact animal.