Abubakar A, Saito T, Kitazawa H, Kawai Y, Itoh T
Laboratory of Animal Products Chemistry, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan.
J Dairy Sci. 1998 Dec;81(12):3131-8. doi: 10.3168/jds.S0022-0302(98)75878-3.
Whey protein was digested with one of seven kinds of proteases at 37 degrees C (trypsin, proteinase K, actinase E, thermolysin, or papain) or at 25 degrees C (pepsin or chymotrypsin) for 24 h. The digested samples were assayed for the inhibitory activity of angiotensin-converting enzyme and for changes in the systolic blood pressure caused in spontaneously hypertensive rats 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 combination 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 18-20), Ile-Pro-Ala (beta-lactoglobulin; f 78-80), Phe-Pro (serum albumin; f 221-222; 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, except an undecapeptide, have antihypertensive activity in spontaneously hypertensive rats. The synthetic tripeptide Ile-Pro-Ala, originating from beta-lactoglobulin, showed the strongest antihypertensive activity (-31 mm Hg).
乳清蛋白分别与七种蛋白酶之一在37℃（胰蛋白酶、蛋白酶K、放线菌酶E、嗜热菌蛋白酶或木瓜蛋白酶）或25℃（胃蛋白酶或胰凝乳蛋白酶）下消化24小时。对消化后的样品进行血管紧张素转换酶抑制活性测定，以及对自发性高血压大鼠胃内插管后收缩压变化的测定。在胃内插管蛋白酶K消化的乳清蛋白6小时后，观察到对收缩压的最强抑制作用（-55 mmHg）。最后，通过疏水反相高效液相色谱和凝胶过滤相结合的方法，从蛋白酶K消化物中色谱分离出六种肽。其氨基酸序列及其来源如下：Val-Tyr-Pro-Phe-Pro-Gly [β-酪蛋白（CN）；f 59-64]，Gly-Lys-Pro（β2-微球蛋白；f 18-20），Ile-Pro-Ala（β-乳球蛋白；f 78-80），Phe-Pro（血清白蛋白；f 221-222；β-CN，f 62-63，f 157-158，和f 205-206），Val-Tyr-Pro（β-CN；f 59-61），以及Thr-Pro-Val-Val-Val-Pro-Pro-Phe-Leu-Gln-Pro（β-CN；f 80-90）。这些六种肽的化学合成证实，除了一种十一肽外，所有肽在自发性高血压大鼠中都具有降压活性。源自β-乳球蛋白的合成三肽Ile-Pro-Ala表现出最强的降压活性（-31 mmHg）。
