Novel angiotensin I-converting enzyme inhibitory peptide derived from bovine casein.

Bovine lactic casein was hydrolysed using a combination of three enzymes, namely, subtilisin, bacillolysin, and trypsin, and the resulting preparation was coined CH-3. CH-3 showed angiotensin I-converting enzyme (ACE)-inhibitory activity (IC50: 74 μg/mL). A single oral administration of CH-3 led to a transient but significant decrease in the systolic blood pressure (SBP) of spontaneously hypertensive rats (SHRs), while daily oral administration of CH-3 for 28 consecutive days led to a lower rate of SBP increase. The CH-3 preparation was then fractionated and the αS2-casein-derived tripeptide Met-Lys-Pro (or MKP) was identified as a novel peptide with strong ACE-inhibitory activity (IC50=0.12 μg/mL, 0.3 μM). The MKP peptide constituted only 0.053% of CH-3 but its activity was accounted for 33% of the total ACE-inhibitory activity of CH-3. In addition, a single oral administration of MKP also led to a transient but significant decrease in the SBP of SHRs.