Subunit interaction elicited by partial inactivation with L-methionine sulfoximine and ATP differently affects the biosynthetic and gamma-glutamyltransferase reactions catalyzed by yeast glutamine synthetase.
Yeast glutamine synthetase can be irreversibly inactivated in the presence of L-methionine sulfoximine, ATP, and a divalent cation Mn2+ or Mg2+. Kinetic studies with partially inactivated enzymes show that inactivation of a given subunit in the octameric glutamine synthetase affects the activities of its neighboring subunit such that the rate of the inactivation as well as the gamma-glutamyltransferase activity of the noninactivated subunits decreases while their biosynthetic activity is enhanced. This outcome of subunit interaction is the same irrespective of whether Mn2+ or Mg2+ is used to fulfill the divalent cation requirement of glutamine synthetase for the inactivation reaction and the gamma-glutamyltransferase reaction. Although only Vmax is affected in the gamma-glutamyltransferase assay, both Km (glutamate) and Vmax are changed in the biosynthetic assay.
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D008717:Methionine Sulfoximine / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D046911:Macromolecular Substances; D008717:Methionine Sulfoximine; D008345:Manganese; D000255:Adenosine Triphosphate; D005723:gamma-Glutamyltransferase; D005974:Glutamate-Ammonia Ligase; D008274:Magnesium