Identification and Characterization of a Gamma-Glutamyl Transpeptidase from a Thermo-Alcalophile Strain of Bacillus pumilus

A γ-glutamyltranspeptidase (GGT, E.C. 2.3.2.2) was isolated from a strain (A8) originating from Lake Bogoria (Kenya) and homologous with Bacillus pumilus. This GGT shows an optimal activity at pH 8.9 and 62°C. The enzyme is thermostable up to 43°C. The best reagent among the potential inhibitors was shown to be DON, which is an inhibitor highly specific for GGTs. Gly-Gly-Ala, Gly-Gly-Gly and Gly-Gly were identified as the best acceptors for the transpeptidation reactions catalyzed by the enzyme. The SDS-PAGE study revealed that the enzyme consists of two non-identical subunits (38,000 and 23,000). Only the large subunit was active when the enzyme was dissociated under denaturing conditions. The behavior of the native enzyme suggests that the active site of the large subunit is masked by the small subunit.