Structural analysis of new antihypertensive peptides derived from cheese whey protein by proteinase K digestion

Whey protein was digested with one of seven kinds of proteases at 37 degree s C (trypsin, proteinase K, actinase E, thermolysin, or papain) or at 25 de grees C (pepsin or chymotrypsin) for 24 h. The digested samples were assaye d for the inhibitory activity of angiotensin-converting enzyme and for chan ges in the systolic blood pressure caused in spontaneously hypertensive rat s after gastric intubation. The strongest depressive effect on the systolic blood pressure (-55 mm Hg) was observed at 6 h after gastric intubation of the whey protein that was digested by proteinase K. Finally, six peptides were chromatographically isolated from the proteinase K digest by a combina tion of hydrophobic reversed-phase HPLC and gel filtration. The amino acid sequences and their origins were clarified as follows: Val-Tyr-Pro-Phe-Pro- Gly [beta-casein (CN); f 59-64], Gly-Lys-Pro (beta(2)-microglobulin; f 18-2 0), Ile-Pro-Ala (beta-lactoglobulin; f 78-80), Phe-Pro (serum albumin; f 22 1-222; beta-CN, f 62-63, f 157-158, and f 205-206), Val-Tyr-Pro (beta-CN; f 59-61), and Thr-Pro-Val-Val-Val-Pro-Pro-Phe-Leu-Gln-Pro (beta-CN; f 80-90) . Chemical synthesis of these six peptides confirmed that all peptides, exc ept an undecapeptide, have antihypertensive activity in spontaneously hyper tensive rats. The synthetic tripeptide Ile-Pro-Ala, originating from beta-l actoglobulin, showed the strongest antihypertensive activity (-31 mm Hg).