J. Biol. Chem., Vol. 262, Issue 27, 13050-13054, 09, 1987

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

KH Kim and SG Rhee
Laboratory of Biochemistry, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20814.

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.
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