Reversible dissociation of gamma-glutamylcysteine synthetase into two subunits.

gamma-Glutamylcysteine synthetase (rat kidney; Mr approximately 104,000) is composed of 2 nonidentical subunits. In the present work, a procedure was developed for the reversible dissociation of the enzyme into its subunits (Mr = 73,000 and 27,700) under nondenaturing conditions. Students in which gel electrophoresis was used, in conjunction with an enzyme activity stain and elution and re-electrophoresis of protein bands, showed that the heavy subunit contains all of the structural requirements for enzymatic activity and also for feedback inhibition of the enzyme activity by glutathione. The light subunit, which may be formed from a precursor protein, has a significantly lower content of Trp, Phe, Tyr, Val, and Ala residues than the heavy subunit, while its content of Lys, His, Met, and Asx residues is higher.