Gene cloning, purification, and characterization of gamma-glutamyltransferase from Pseudomonas syringae (PsGGT) were performed in Escherichia coli. PsGGT was partially purified to 13-fold, with a specific activity of 0.92 U/mg. The molecule is presumed to be a heterodimeric consisting of large (37 kDa) and small (21 kDa) subunits. The optimal pH and temperature for hydrolytic activity were 8 and 37 A degrees C, and those for transfer activity were 9 and 50 A degrees C, respectively. PsGGT could transfer beta-aspartyl moiety from asparagine to hydroxylamine and the gamma-glutamyl moiety from glutamine to hydroxylamine. PsGGT demonstrated novel functionality on both gamma-glutamyltransferase and beta-aspartyltransferase.