title: Regulation of glutamine synthetase from Saccharomyces cerevisiae by repression, inactivation and proteolysis.
abstract: Glutamine synthetase activity is modulated by nitrogen repression and by two distinct inactivation processes. Addition of glutamine to exponentially grown yeast leads to enzyme inactivation. 50% of glutamine synthetase activity is lost after 30 min (a quarter of the generation time). Removing glutamine from the growth medium results in a rapid recovery of enzyme activity. A regulatory mutation (gdhCR mutation) suppresses this inactivation by glutamine in addition to its derepressing effect on enzymes involved in nitrogen catabolism. The gdhCR mutation also increases the level of proteinase B in exponentially grown yeast. Inactivation of glutamine synthetase is also observed during nitrogen starvation. This inactivation is irreversible and consists very probably of a proteolytic degradation. Indeed, strains bearing proteinase A, B and C mutations are no longer inactivated under nitrogen starvation.
mesh_terms: D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009584:Nitrogen / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen