Stimulation of hepatic glutathione formation by administration of L-2-oxothiazolidine-4-carboxylate, a 5-oxo-L-prolinase substrate.

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Abstract
5-Oxo-L-prolinase [from rat kidney], the enzyme that catalyzes the conversion of 5-oxo-L-proline to L-glutamate coupled to the cleavage of ATP to ADP and Pi, also acts on L-2-oxothiazolidine-4-carboxylate (an analog of 5-oxoproline in which the 4-methylene moiety is replaced by sulfur) and ATP to yield cysteine and ADP. The enzyme, which exhibits an affinity for the analog similar to that for the natural substrate, is inhibited by the analog in vitro and in vivo. L-2-Oxothiazolidine-4-carboxylate serves as a potent inhibitor of the .gamma.-glutamyl cycle at the step of 5-oxoprolinase. Administration of L-2-oxothiazolidine-4-carboxylate to mice that had been depleted of hepatic glutathione led to restoration of normal hepatic glutathione levels. Since L-2-oxothiazolidine-4-carboxylate is an excellent substrate of the enzyme, it may serve as an intracellular delivery system for cysteine and has potential as a therapeutic agent for conditions in which there is depletion of hepatic glutathione.