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Rat Liver Glutathione: Possible Role as a Reservoir of Cysteine¹

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

Rat liver contains a high concentration (7–8 mM) of reduced glutathione and its level changes rapidly when starving or feeding rats. We concluded that one of the functions of liver glutathione was to act as a reservoir of cysteine. When starved rats were fed a protein-free diet, the increase in liver glutathione was dependent on the amount of cysteine added to the diet. A cysteine-dependent increase of glutathione was also observed in rats fed a diet containing gelatin with cysteine, but the increase was relatively lowered compared with rats fed a protein-free diet containing the same amount of cysteine. This suppression of the increase in glutathione was observed much more clearly when the gelatin diet was fortified with tryptophan in addition to cysteine. In the presence of tryptophan, L-[³⁵S]-cysteine in the diet appeared to be incorporated primarily into liver and serum proteins, and degradation of liver glutathione must also have been enhanced. Addition of excess cysteine to the diet masked the effects of gelatin and tryptophan, and stimulated glutathione synthesis in the liver as well as incorporation of dietary cysteine into protein fractions. Prolonged starvation of rats or injection of dibutyryl-3',5'-cyclic AMP lowered the glutathione level, but the level did not decrease below 2 to 3 mM. These findings suggest that there may be at least two pools of glutathione. A labile fraction, constituting one-third to one-half the total liver glutathione, probably serves as a reservoir of cysteine which can be released by -glutamyltransferase when necessary.

KEY WORDS: • liver glutathione • dietary cysteine • liver protein synthesis • polysome profiles

¹ Part of this work was presented orally at the Xth International Congress of Nutrition in August, 1975 (Kyoto). The work was supported in part by grants from the Yamanouchi Pharmaceutical Co., Tokyo and the Kanae Foundation of the New Medicine Research Association, Tokyo.

² Requests for reprints should be sent to Dr. Noriko Tateishi.

Manuscript received 29 December 1975.

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