UPTAKE AND METABOLISM OF L-2-OXO-[S-35]THIAZOLIDINE-4-CARBOXYLATE BY RAT-CELLS IS SLOWER THAN THAT OF L-[S-35]CYSTEINE OR L-[S-35]METHIONINE

The uptake and metabolism of L-2-oxo-[S-35]thiazolidine-4-carboxylate (OTC) was compared with that of L-[S-35]cysteine and L-[S-35]methionine in studies with freshly isolated rat hepatocytes, renal cortical tubules and enterocytes. All three S-35-labeled substrates were metabolized to glutathione, inorganic sulfur and taurine by hepatocytes and to inorganic sulfur by renal tubules and enterocytes. The rate of metabolite production from OTC was always < 30% of that from cysteine or methionine. The transport rate for uptake of [S-35]OTC by hepatocytes was less than that observed for uptake of [S-35]cysteine or [S-35]methionine. The capacity of rat hepatocytes, renal cortical tubules and enterocytes to take up and metabolize OTC is substantially lower than that for uptake and metabolism of cysteine or its normal intracellular precursor, methionine.