Characterization of extracellular γ-glutamyl transpeptidase from Aspergillus nidulans

Aspergillus nidulans γ-glutamyl transpeptidase (AnγGT, EC 2.3.2.2) was partially purified from the fermentation broth of carbon stressed cultures. Its temperature and pH optimum was 45 °C and pH 8.0, respectively. AnγGT had little hydrolase activity. It utilized Gln, glutathione and less efficiently oxidized glutathione as γ-glutamyl donors (beside of γ-glutamyl-p-nitroanilide) and amino-acids and peptides (including Glu, Cys, Met, Gly-Gly and Cys-Gly) but not hydroxylamine as γ-glutamyl acceptors. We propose that the function of this enzyme is not to degrade, but to produce, γ-glutamyl compounds which may be related to the utilization of extracellular peptides and amino-acids in carbon stressed cultures.