Purification and properties of two isozymes of gamma-glutamyltranspeptidase from Bacillus subtilis TAM-4

Two isozymes of gamma-glutamyltranspeptidase, GGT-A and GGT-B, were purified to electrophoretic homogeneity from a culture broth of Bacillus subtilis TAM-4, which produces poly(gamma-glutamic acid) (PGA) de novo. GGT-A was composed of three subunits with molecular weights of 23,000 (I), 39,000 (II), and 40,000 (III). GGT-B was composed of two subunits with molecular weights of 22,000 (I) and 39,000 (II). The N-terminal amino acid sequences of GGT-A subunit I and GGT-B subunit I were very similar, GGT-A subunit II and GGT-B subunit II had an identical N-terminal amino acid sequence, That of GGT-A subunit III showed no similarity to the other subunits, Both GGTs had similar enzymatic properties (optimum pH and temperature: pH 8.8 and 55 degrees C) but showed a significantly different thermal stability at 55 degrees C, Both GGT-A and -B used D-gamma-glutamyl-p-nitroanilide as well as the L-isomer as the gamma-glutamyl donor and used various amino acids and peptides as the acceptor, It was also found that the PGA produced by the strain was hydrolyzed to glutamic acid by its own GGTs.