PURIFICATION AND CHARACTERIZATION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE FROM ASCARIS-SUUM

gamma-Glutamyl transpeptidase, which is of central importance in the d egradation of glutathione, was purified from Ascaris suum to apparent homogeneity. The enzyme was found to be a predominantly membrane-bound protein and was solubilized by Triton X-100. The purified enzyme, whi ch exhibits a specific activity of 1009 U (mg protein)(-1), showed a m olecular mass of 70 kDa and was found to be composed of two non-identi cal subunits of molecular mass 43 and 30 kDa. Concerning the kinetic p roperties of the enzyme, the data presented in this study showed that various amino acids and dipeptides with L-configuration served as acce pters for the gamma-glutamyl moieties of the enzyme reaction products and showed K-m-values in the mM range. The apparent K-m-value for the gamma-glutamyl donor L-glutamyl-gamma-7-amido-4-methylcoumarin of the enzyme was found to be 0.03 mM. L- and D-serine in combination with bo rate ions were competitive inhibitors of the enzyme activity with K-i- values of 0.30 and 0.61 mM, respectively. Acivicin was an irreversible inhibitor of the enzyme with a K-i-value of 0.42 mM and with a pseudo -first-order kinetics (k(inact)) of 0.18 min(-1). In vitro treatment o f the adult A. suum with acivicin resulted in a dose-dependent inhibit ion of the enzyme activity and an increase of the glutathione levels. These findings indicate the physiological role of the gamma-glutamyl t ranspeptidase of this parasitic nematode in the catabolism of glutathi one.