An X-prolyl-dipeptidyl peptidase has been purified from Lactobacillus sakei by ammonium sulfate fractionation and five chromatographic steps, which included hydrophobic interaction, anion-exchange chromatography, and gel filtration chromatography, This procedure resulted in a recovery yield of 7% and an increase in specificity of 737-fold. The enzyme appeared to be a dimer,vith a subunit molecular mass of approximately 88 kDa, Optimal activity was shown at pH 7.5 and 55 degreesC. The enzyme was inhibited by serine proteinase inhibitors and several divalent cations (Cu2+, Hg2+, and Zn2+). The enzyme almost exclusively hydrolyzed X-Pro from the N terminus of each peptide as well as fluorescent and colorimetric substrates; it also hydrolyzed X-Ala at the N terminus, albeit at lower rates. K-m s for Gly-Pro- and Lys-Ala-7-amido-4-methylcoumarin were 29 and 88 IJ M, respectively; those for Gly-Pro- and Ala-Pro-p-nitroanilide were 192 and 50 muM, respectively. Among peptides, beta -casomorphin 1-3 was hydrolyzed at the highest rates, while the relative hydrolysis of the other tested peptides was only 1 to 12%, The potential role of the purified enzyme in the proteolytic pathway by catalyzing the hydrolysis of peptide bonds involving proline is discussed.ALI97-0353 from CICYT (Spain)