Shammet K M, Brown R J, McMahon D J
Department of Nutrition and Food Sciences, Utah State University, Logan 84322-8700.
J Dairy Sci. 1992 Jun;75(6):1380-8. doi: 10.3168/jds.S0022-0302(92)77890-4.
Proteolytic activities of chymosin, bovine pepsin, Mucor miehei rennet, Cryphonectria parasitica (formerly Endothia parasitica) rennet, trypsin, and chymotrypsin on kappa-casein macropeptide were measured. Macropeptide solutions (10 mg/ml of .05 M, pH 6.6 phosphate buffer) were incubated with the enzymes at 37 degrees C for various times, and their reactions were stopped by adding .025 ml of pepstatin (1 mg/ml of methanol). Peptides released from kappa-casein macropeptide were then fractionated using reverse-phase HPLC. At the pH of milk (pH 6.6), kappa-casein macropeptide was resistant to enzymic action by chymosin, bovine pepsin, and M. miehei and C. parasitica rennets. Bovine pepsin hydrolyzed kappa-casein macropeptide at pH 3. kappa-Casein macropeptide was readily hydrolyzed at pH 6.6 by trypsin and chymotrypsin. Possible physiological functions of the kappa-casein macropeptide are discussed in light of these findings.
测定了凝乳酶、牛胃蛋白酶、米黑毛霉凝乳酶、寄生隐孢霉（原寄生内座壳）凝乳酶、胰蛋白酶和胰凝乳蛋白酶对κ-酪蛋白大肽的蛋白水解活性。将大肽溶液（10 mg/ml的0.05 M，pH 6.6磷酸盐缓冲液）与酶在37℃孵育不同时间，通过加入0.025 ml胃蛋白酶抑制剂（1 mg/ml甲醇）终止反应。然后使用反相高效液相色谱法对从κ-酪蛋白大肽释放的肽进行分离。在牛奶的pH值（pH 6.6）下，κ-酪蛋白大肽对凝乳酶、牛胃蛋白酶以及米黑毛霉和寄生隐孢霉凝乳酶的酶促作用具有抗性。牛胃蛋白酶在pH 3时可水解κ-酪蛋白大肽。κ-酪蛋白大肽在pH 6.6时易被胰蛋白酶和胰凝乳蛋白酶水解。根据这些发现讨论了κ-酪蛋白大肽可能的生理功能。
