Purification and Characterization of a Tripeptidase from Lactococcus lactis subsp. cremoris Wg2

A tripeptidase from a cell extract of Lactococcus lactis subsp. cremoris Wg2 has been purified to homogeneity by DEAE-Sephacel and phenyl-Sepharose chromatography followed by gel filtration over a Sephadex G-100 SF column and a high-performance liquid chromatography TSK G3000 SW column. The enzyme appears to be a dimer with a molecular weight of between 103,000 and 105,000 and is composed of two identical subunits each with a molecular weight of about 52,000. The tripeptidase is capable of hydrolyzing only tripeptides. The enzyme activity is optimal at pH 7.5 and at 55 degrees C. EDTA inhibits the activity, and this can be reactivated with Zn, Mn, and partially with Co. The reducing agents dithiothreitol and beta-mercaptoethanol and the divalent cation Cu inhibit tripeptidase activity. Kinetic studies indicate that the peptidase hydrolyzes leucyl-leucyl-leucine with a K(m) of 0.15 mM and a V(max) of 151 mumol/min per mg of protein.