The γ-Glutamyl Cycle and Amino Acid Transport

Abstract

EVIDENCE is accumulating that the tripeptide glutathione (γ-glutamyl-cysteinyL-glycine) participates in a variety of fundamental processes such as intracellular redox reactions, active transport of amino acids and protection against free radicals generated by high-energy irradiation, oxidative stress or drug metabolism.^{1 , 2} The enzymes involved in the metabolism of glutathione are functionally integrated in the γ-glutamyl cycle³ (Fig. 1). Clinical medicine has added to knowledge of the function of glutathione through observations on patients with inborn errors of glutathione synthesis. Thus, a deficiency of γglutamyl-cysteine synthetase⁴ or glutathione synthetase^{5 6 7 8} in erythrocytes has been identified as a cause of hemolytic anemia.A generalized deficiency . . .