Angiotensin I-converting enzyme inhibitor derived from an enzymatic hydrolysate of casein. II. Isolation and bradykinin-potentiating activity on the uterus and the ileum of rats.

Inhibitors of angiotensin I-converting enzyme were isolated from an enzymatic hydrolysate of bovine casein. The amino acid sequences of these inhibitors were Phe-Phe-Val-Ala-Pro-Phe-Pro-Glu-Val-Phe-Gly-Lys (CEI12), Phe-Phe-Val-Ala-Pro (CEI5), and Ala-Val-Pro-Tyr-Pro-Gln-Arg (CEIβ7). CEI5 is a penta-peptide derived from the hydrolysate of CEI12 with proline-specific endopeptidase, and CEIβ7 is a hepta-peptide derived from β-casein. These inhibitors potentiated bradykinin in the contraction of the uterus and the ileum of rats. The ileum was more sensitive to these inhibitors than the uterus. The bradykinin-potentiating activity of these inhibitors on the ileum lasted for more than 90 min even after washing the organ.