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A prolyl aminopeptidase (PAP) (EC 3.4.11.5) was isolated from the cell extract of Debaryomyces hansenii CECT12487. The enzyme was purified by selective fractionation with protamine and ammonium sulfate, followed by two chromatography steps, which included gel filtration and anion-exchange chromatography. The PAP was purified 248-fold, with a recovery yield of 1.4%. The enzyme was active in a broad pH range (from 5 to 9.5), with pH and temperature optima at 7.5 and 45°C. The molecular mass was estimated to be around 370 kDa. The presence of inhibitors of serine and aspartic proteases, bestatin, puromycin, reducing agents, chelating agents, and different cations did not have any effect on the enzyme activity. Only iodoacetate, p -chloromercuribenzoic acid, and Hg 2+ , which are inhibitors of cysteine proteases, markedly reduced the enzyme activity. The K m for proline-7-amido-4-methylcoumarin was 40 μM. The enzyme exclusively hydrolyzed N-terminal-proline-containing substrates. This is the first report on the identification and purification of this type of aminopeptidase in yeast, which may contribute to the scarce knowledge about D. hansenii proteases and their possible roles in meat fermentation.

Strains of Lactobacillus plantarum originally isolated from sausages were screened for proteinase and aminopeptidase activities toward synthetic substrates; on the basis of that screening, L. plantarum CRL 681 was selected for further assays on muscle proteins. The activities of whole cells, cell extracts (CE), and a combination of both on sarcoplasmic and myofibrillar protein extracts were determined by protein, peptide, and free-amino-acid analyses. Proteinase from whole cells initiated the hydrolysis of sarcoplasmic proteins. The addition of CE intensified the proteolysis. Whole cells generated hydrophilic peptides from both sarcoplasmic and myofibrillar proteins. Other peptides of a hydrophobic nature resulted from the combination of whole cells and CE. The action of both enzymatic sources on myofibrillar proteins caused maximal increases in lysine, arginine, and leucine, while the action of those on sarcoplasmic proteins mainly released alanine. In general, pronounced hydrolysis of muscle proteins required enzyme activities from whole cells in addition to those supplied by CE.

Lactobacillus curvatus CECT 904 and Lactobacillus sake CECT 4808 were selected on the basis of their proteolytic activities against synthetic substrates. Further, the effects of whole cells, cell extracts, and a combination of both enzymatic sources on muscle sarcoplasmic proteins were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse-phase high-performance liquid chromatography analyses. Strains of both species displayed proteinase activities on five sarcoplasmic proteins. The inoculation of whole cells caused a degradation of peptides, whereas the addition of cell extracts resulted in the generation of both hydrophilic and hydrophobic peptides. This phenomenon was remarkably more pronounced when L. curvatus was involved. Whole cells also consumed a great amount of free amino acids, while the addition of intracellular enzymes contributed to their generation. L. sake accounted for a greater release of free amino acids. In general, cell viability and also proteolytic events were promoted when cell suspensions were provided with cell extracts as an extra source of enzymes.