AN IMPORTANT ROLE FOR GLUTATHIONE AND GAMMA-GLUTAMYL-TRANSPEPTIDASE IN THE SUPPLY OF GROWTH REQUIREMENTS DURING NITROGEN STARVATION OF THE YEAST SACCHAROMYCES-CEREVISIAE

When the yeast Saccharomyces cerevisiae Sigma 1278b was starved for ni trogen, the total glutathione (GSH) pool increased from 7 to 17 nmol ( mg dry wt)(-1) during the first 2 h and then declined. More than 90% o f the total GSH shifted towards the central vacuole during this time. This transient stimulation was not observed in the presence of buthion ine-(S,R)-sulphoximine (BSO), a specific transition-state-analogue inh ibitor of gamma-glutamylcysteine synthase (gamma-GCS), nor in a mutant strain deficient in this enzyme. gamma-Glutamyltranspeptidase (gamma- GT), a vacuolar enzyme responsible for the initial step of GSH degrada tion, was derepressed during nitrogen starvation. This mechanism can a pparently enable the starved yeast cell to use the constituent amino a cids from GSH which accumulate in the vacuole to satisfy its growth re quirements for nitrogen.