Proteolytic Activity of Proteinases on Macropeptide Isolated from -Casein

¹ Department of Nutrition and Food Sciences, Utah State University, Logan 84322-8700

Proteolytic activities of chymosin, bovine pepsin, Mucor miehei rennet, Cryphonectria parasitica (formerly Endothia parsitica) rennet, trypsin, and Chymotrypsin on -casein macropeptide were measured. Macropeptide solutions (10 mg/ml of .05 M, pH 6.6 phosphate buffer) were incubated with the enzymes at 37°C for various times, and their reactions were stopped by adding .025 ml of pepstatin (1 mg/ml of methanol). Peptides released from -casein macropeptide were then fractionated using reverse-phase HPLC. At the pH of milk (pH 6.6). -casein macropeptide was resistant to enzymic action by chymosin, bovine pepsin, and M. miehei and C. parasitica rennets. Bovine pepsin hydrolyzed -casein macropeptide at pH 3. -Casein macropeptide was readily hydrolyzed at pH 6.6 by trypsin and chymotrypsin. Possible physiological functions of the -casein macropeptide are discussed in light of these findings.

Key Words: -casein • proteinase • macropeptide

Submitted on January 14, 1991
Accepted on February 18, 1992

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