γ-Glutamyl transpeptidase, which is of central importance in the degradation 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, which exhibits a specific activity of 1009 U (mg protein)−1, showed a molecular mass of 70 kDa and was found to be composed of two non-identical subunits of molecular mass 43 and 30 kDa. Concerning the kinetic properties of the enzyme, the data presented in this study showed that various amino acids and dipeptides with L-configuration served as acceptors for the γ-glutamyl moieties of the enzyme reaction products and showed Km-values in the mM range. The apparent Km-value for the γ-glutamyl donor L-glutamyl-γ-7-amido-4-methylcoumarin of the enzyme was found to be 0.03 mM. L- and D-serine in combination with borate ions were competitive inhibitors of the enzyme activity with Ki-values of 0.30 and 0.61 mM, respectively. Acivicin was an irreversible inhibitor of the enzyme with a Ki-value of 0.42 mM and with a pseudo-first-order kinetics (kinact) of 0.18 min−1. In vitro treatment of the adult A. suum with acivicin resulted in a dose-dependent inhibition of the enzyme activity and an increase of the glutathione levels. These findings indicate the physiological role of the γ-glutamyl transpeptidase of this parasitic nematode in the catabolism of glutathione.

Title

Molecular and Biochemical Parasitology Volume 77, Issue 1, April 1996, Pages 41-47

Publisher

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Publisher Country

Palestine

Publication Type

Both (Printed and Online)

Volume

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Year

2009

Pages

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