[Assay and normal levels of L-glutamate-L-cysteine-gamma-ligase (E.C. 6.3.2.2) in human erythrocytes; biosynthesis of glutathione V].

For the determination of the activity of glutamate: cysteine-gamma-ligase one method was optimized and a new micromethod was developed: a) Utilizing [14C] glutamate and cysteine as substrates, the product [14C] gamma-glutamylcysteine was isolated as its cadmium mercaptide and determined by liquid scintillation counting gamma-glutamyl-[14C] aminobutyrate, which was synthesized from glutamate and [14C] alpha-aminobutyrate was separated from remaining radioactive substrate by paper electrophoresis and counted. Both methods were used to determine the activity of the enzyme in human red blood cells. For 20 parallel determinations a standard deviation of +/- 9% and +/- 5% was obtained for method a and b, respectively. The specific activity of the enzyme in erythrocytes of adults was found to be 0.40 +/- 0.05 U/g hemoglobin with method a, and 0.50 +/- 0.05 U/g hemoglobin with method b.