The maximum activities of the enzymes for the biosynthesis of GSH (gamma-glutamyl-cysteine synthetase and GSH synthetase) have been assayed in high GSH and low GSH erythrocytes from Tasmanian Merino and Finnish Landrace sheep. 2. For the Merinos, the activities (mumol product/g haemoglobin per min +/- S.E.M. (n)) in the high and low GSH erythrocytes respectively were: gamma-glutamyl-cysteine synthetase: 0.776 +/- 0.065 (11) and 0.375 +/- 0.063 (13); and GSH synthetase: 0.069 +/- 0.003 (11) and 0.066 +/- 0.002 (13). 3. For the Finnish Landrace sheep the activities in the high and low GSH erythrocytes respectively were: gamma-glutamyl-cysteine synthetase: 0.595 +/- 0.063 (12) and 0.555 +/- 0.033 (10) and gamma-glutamyl-cysteine synthetase: 0.073 +/- 0.002 (12) and 0.070 +/- 0.002 (10). 4. gamma-Glutamyl-cysteine synthetase was markedly inhibited by physiological GSH concentrations. No evidence was found for the presence of an inhibitor of GSH biosynthesis (other than GSH) in low GSH erythrocytes from Finnish Landrace sheep. 5. Although for the Merinos the low GSH trait can be explained in terms of a diminished activity of gamma-glutamyl-cysteine synthetase, no such explanation is tenable for the Finnish Landrace sheep.
