Properties of Glycomacropeptide and Para-K-casein Derived from Human κ-Casein and Comparison of Humanand Bovine κ-Caseins as to Susceptibility to Chymosin and Pepsin

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Soluble and insoluble portions obtained after chymosin treatment of purified humanK>casein were isolated by CM-Sephadexcation exchange chromatography. The soluble portion included all sugars present in intact human κ-casein and the insoluble portion was devoid of sugars. They were designated as human glycomacropeptide and para-κ-casein following the example of bovine κ-casein. The results of amino acid analyses showed that humanglycomacropeptide contained a large amount of acidic amino acids and a small amount of basic amino acids (His and Arg were not contained). Onthe other hand, para-κ-casein contained both acidic and basic amino acids. Human para-κ-casein was positively charged at pH 8.6 and migrated toward the cathode on polyacrylamide gel electrophoresis. Kinetic parameters (Km) for the chymosin action on human and bovine κ-caseinswere 10.6×10-5M and 6.6×10-5M, and thoseforthepepsinactionwere 5.2×10-5M and 4.0×10-5M, respectively.
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