Purification and properties of dipeptidase from Escherichia coli AJ005

A Co2+-dependent dipeptidase from E. coli strain AJ005, a peptidase-deficient mutant, was purified with streptomycin sulfate, ammonium sulfate and DEAE-cellulose. The purified dipeptidase increased by about 106-fold in specific activity, with dilysine as a substrate. The dipeptidase cleaved dilysine to two lysines among the lysine homopolymers, the possibility remaining that it is active toward peptides other than dilysine, since it was investigated in the present study only for activity toward lysine homopolymers. Activity was inhibited 54% by 10(-3) M KCN and completely by 10(-3) M PCMB, EDTA and benzethonium chloride, but not at all by soybean trypsin inhibitors. 78% and 95% of its activity was lost with 30 minutes' treatment at 45 degrees C and 50 degrees C, respectively. The apparent Km value was 6.7 X 10(-4) M for dilysine. It is probable that the dipeptidase differs from dipeptidase DP.