Inhibition of the hydrolytic and transpeptidase activities of rat kidney gamma-glutamyl transpeptidase by specific monoclonal antibodies

Monoclonal antibodies (mAb) against the native form of rat kidney gamma-glu tamyl transpeptidase (GGT) were isolated by screening hybridomas with rat k idney brush-border membrane vesicles. They were directed against protein ra ther than sugar epitopes in that each recognized all GGT isoforms. All of t hem inhibited partially the enzyme activity of GGT. They were specific in t hat they inhibited the rat enzyme, but not the mouse or human enzyme. Kinet ic analyses were carried out with free GGT and GGT-mAb complexes with D-gam ma-glutamyl-p-nitroanilide in the presence or absence of maleate, or in the presence or absence of alanine, cysteine, cystine or glycylglycine as gamm a-glutamyl accepters. mAbs 2A10 and 2E9 inhibited the hydrolytic and glutam inase activities of GGT and had little effect on the transpeptidation activ ity of the enzyme, whereas mAbs 4D7 and 5F10 inhibited transpeptidation, bu t not hydrolytic or glutaminase activities, mAb 5F10 mimicked the effect of maleate on GGT, in that it inhibited transpeptidation, enhanced the glutam inase activity and increased the affinity of the donor site of GGT for aciv icin. Such mAbs may be useful for long-term studies in tissue cultures and in vivo, and for the identification of GGT epitopes that are important for the hydrolytic and transpeptidase activities.