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 with a subunit molecular mass of approximately 88 kDa. Optimal activity was shown at pH 7.5 and 55°C. The enzyme was inhibited by serine proteinase inhibitors and several divalent cations (Cu 2؉ , Hg 2؉ , and Zn
2؉). 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 M, respectively; those for Gly-Pro-and Ala-Pro-p-nitroanilide were 192 and 50 M, respectively. Among peptides, -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.Lactic acid bacteria constitute one of the most important group of microorganisms used in food fermentation. In the last decades, the metabolic traits of these bacteria have been the object of exhaustive studies, which evidence promising applications (12). The proteolytic properties of dairy lactic acid bacteria are among the best characterized to date (5, 13). This is a consequence of the impact of proteolysis on the physiology of these organisms as well as on the development of texture and flavor of dairy products (6, 18). Proteolysis on milk proteins is initiated by a cell wall-associated proteinase, which hydrolyzes caseins into oligopeptides. The generated peptides are mainly translocated via the oligopeptide transport system and, further, hydrolyzed by a pool of intracellular peptidases, which include endopeptidases, aminopeptidases, dipeptidases, tripeptidases, and dipeptidyl peptidases (13).Lactobacillus sakei is the most competitive species in meat fermentation and therefore constitutes a frequently used starter culture. The proteolytic events that occur during meat processing also lead to the generation of small peptides and free amino acids, which are considered to be flavor compounds (1, 31). In fermented meat products, muscle as well as microbial enzymes are responsible for the proteolytic changes, but their roles remain elusive (21, 31). Particularly, the studies on the proteolytic system of meat lactobacilli are rather limited. It has been shown that several Lactobacillus spp. exhibit proteolytic activity on porcine muscle myofibrillar and sarcoplasmic proteins (7,8,28). These studies highlighted the potential role of L. sakei in amino acid and peptide generation especially from sarcoplasmic proteins. Attention has also been focused on intracellular peptidases of L. ...