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The L-Methionine-Sparing Effect of Dietary Glutathione in Rats^1,2,

Department of Biochemistry, Institute for Cancer Research, Osaka University Medical School, 1-1-50, Fukushima, Fukushima-ku, Osaka 553, Japan

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.

KEY WORDS: • methionine-sparing effect • methionine • cysteine • glutathione • liver protein • plasma protein

¹ A part of this work was presented orally at the International Symposium on "Glutathione-Storage, Transport and Turnover in Mammals" held on December 11, 1981 in Osaka, Japan [to be published by Japan Sci. Soc. Press (Sakamoto, Y., Higashi, T. & Tateishi, N., eds.)] and at the 5th Karolinska Institute Nobel Conference "Functions of Glutathione—Biochemical, Physiological and Toxicological Aspects" held on May 23–27, 1982 in Skokloster, Sweden [to be published by Raven Press, New York (Larsson, A., Orrenius, S. & Holmgren, A., eds.) in 1983].

² This work was supported by a Grant-in-Aid for Scientific Research (No. 57580031) from the Ministry of Education, Science and Culture of Japan and in part by the Yamanouchi Pharmaceutical Co., Ltd.

Manuscript received 20 January 1982.