Affinity labeling of gamma-glutamyl transpeptidase and location of the gamma-glutamyl binding site on the light subunit

Abstract

Gamma-Glutamyl transpeptidase, which consists of two nonidentical subunits, is rapidly inactivated with respect to its transpeptidase and hydrolase activities by the gamma-glutamyl analogs 6-diazo-5-oxo-L-norleucine and L-azaserine. Inactivation, which is prevented by gamma-glutamyl substrates (but not by acceptor substrates), is accelerated by maleate, which was previously shown to enhance utilization of glutamine by transpeptidase. 6-Diazo-5-oxo--norleucine reacts specifically, covalently, and stoichiometrically at the gamma-glutamyl site of the enzyme, which was localized through studies with 6-diazo-5-OXO-[14C]norleucine to the light subunits of both the transpeptidase of rat kidney (which has subunits of molecular weights 22,000 and 46,000) and the transpeptidase of human kidney (which has subunits of molecular weights 22,000 and 62,000). The findings, which indicate that these enzymes have similar gamma-glutamyl binding subunits, are relevant to the structure-function relationships of this membrane-bound enzyme and its physiological role.