When the yeast Σ1278b was starved for nitrogen, the total glutathione (GSH) pool increased from 7 to 17 nmol (mg dry wt) during the first 2 h and then declined. More than 90% of the total GSH shifted towards the central vacuole during this time. This transient stimulation was not observed in the presence of buthionine-()-sulphoximine (BSO), a specific transition-state-analogue inhibitor of γ-glutamylcysteine synthase (γ-GCS), nor in a mutant strain deficient in this enzyme. γ-Glutamyltranspeptidase (γ-GT), a vacuolar enzyme responsible for the initial step of GSH degradation, was derepressed during nitrogen starvation. This mechanism can apparently enable the starved yeast cell to use the constituent amino acids from GSH which accumulate in the vacuole to satisfy its growth requirements for nitrogen.


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