The aminopeptidase C (PepC) from Lactobacillus helveticus CNRZ32. A comparative study of PepC from lactic acid bacteria

The aminopeptidase C (PepC) of Lactobacillus helveticus CNRZ32 was purified by anion exchange chromatography from cell free extracts of an E. coli DH5 alpha clone overexpressing the Lactobacillus aminopeptidase. PepC was foun d to have a tetrameric structure in its native form with subunits of 50 kDa each, a pH optimum of 6.5 and maximum activity at 45 degreesC. Sulfhydryl- blocking reagents inhibited the enzyme activity whereas reducing or metal c helating reagents had an activating effect on the PepC activity. The PepC h ydrolyzed a wide range of p-nitroaniline derivatives, dipeptides and severa l tripeptides which contained basic amino acids (Arg, Lys), Pro residues, o r cheese flavour precursor amino acids (Met, Leu, Phe) at the N-terminal po sition. The substrate specificity and residual activity of PepC from severa l lactic acid bacteria, including the PepC described above, were compared a t conditions of pH and NaCl present in cheese.