γ-glutamyl transpeptidase (GGT) from Onchocerca volvulus is involved in the oxidative stress. The enzyme catalyzes the breakdown of glutathione (GSH) and thus provide the parasite with cysteine for the synthesis of GSH and other amnio acids. The enzyme, which was highly purified from Onchocerca volvulus, is found to be membrane-bound with a specific activity of 100 U mg-1 and a molecular mass of 68 KDa.  The apparent Km-values for the γ-glutamyl donor  L-glutamic acid γ-(4-nitroanilide) is 0.023 ± 0.013 mM. The data presented in this study showed that various amino acids and dipeptides served for the γ-glutamyl moieties of the enzyme reaction products and showed Km values in the mM range. Acivicin was an irreversible inhibitor of the enzyme with a pseudo-first-order kinetics (kmax) of 0.34 ± 0.004 min−1 and KI = 0.59 ± 0.04 mM. These finding indicate the physiological role of the GGT of this parasite nematode in the catabolism of GSH. Further studies are required to investigate the use of this enzyme as a potential target for the development of chemotherapy against O. volvulus.

Keywords: γ-glutamyl transpeptidase, Onchocerca volvulus, acivicin, Glutathione