Purification and characterization of an endopeptidase that has an important role in the carboxyl terminal processing of antihypertensive peptides in Lactobacillus helveticus CM4

Aims: To purify and characterize a peptidase that can catalyse C-terminal processing of antihypertensive peptide from Lactobacillus helveticus CM4. Methods and Results: An endopeptidase which seems to process the carboxyl terminal end of two antihypertensive peptides, Val-Pro-Pro and Ile-Pro-Pro, was purified from Lactobacillus helveticus CM4 by four stages of column chromatography, using synthetic pro-peptide as a substrate. The molecular weight of the purified enzyme was estimated to be 67 000 by SEPHACRYL S-200 and 70 000 by SDS-PAGE analysis. The purified enzyme generated: (i) Val-Pro-Pro from Val-Pro-Pro-Phe-Leu and Val-Pro-Pro-Phe-Leu-Gln-Pro, and (ii) Ile-Pro-Pro from Ile-Pro-Pro-Leu-Thr and Ile-Pro-Pro-Leu-Thr-Gln-Thr, but theses peptides could not be generated from Val-Pro-Pro-Phe, Val-Pro-Pro-Phe-Leu-Gln, Ile-Pro-Pro-Leu and Ile-Pro-Pro-Leu-Thr-Gln. Part of the amino terminal sequence of the purified enzyme had homology to a previously reported pepO gene product. Conclusion: These results suggest that the purified endopeptidase isolated in this study have an important role in the carboxyl terminal processing of two antihypertensive peptides in Lact. helveticus CM4.