The L-methionine-sparing effect of dietary glutathione in rats

The availability of cysteine moiety released from dietary glutathione (GSH) for protein synthesis in rats was studied to determine the L-methionine-sparing effect of this peptide. Animals were fed diets containing 18% of an amino acid mixture having a composition similar to that of whole egg, with or without GSH. The proportions of L-methionine, L-cysteine and GSH in the diet were varied, and one of these components was labeled with 35S. The incorporation of label into proteins and GSH in the liver and into proteins in the plasma was determined to assess the utilization of the sulfur atoms in these sulfur-containing substances. Dietary [35S]GSH was found to be incorporated efficiently into proteins and GSH in the liver and into plasma proteins. The results demonstrate the L-methionine-sparing effect of dietary GSH, in terms of incorporation Of its 35S into proteins and GSH. GSH spared L-methionine almost as efficiently as L-cysteine in plasma protein synthesis, though slightly less in liver protein synthesis. The effect of GSH increased with increase in its concentration in the diet.