Abstract
To understand the mechanism by which γ-polyglutamic acid (γ-PGA) in the sticky material of natto was synthesized, we purified the γ-glutamyltranspeptidase (γ-GTP) (EC 2.3.2.2) from the culture broth of Bacillus subtilis (natto) to homogeneity. γ-GTP was composed of two subunits with molecular weight of 45, 000 and 22, 000. The N-terminal amino acid sequence of light subunit was homologous with that of γ-GTP from Escherichia coli. The optimum pH and temperature of activity were 8.5 and 60°C. The enzyme was inactivated by incubation for 15 min at pH 8.0 and 55°C, but little loss of the activity was detected at 40°C. γ-GTP used glutamine as a γ-glutamyl donor and acceptor for γ-PGA synthesis. Dipeptides were better γ-glutamyl acceptors than free amino acids.
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