Presence of O-glycosidic linkage through serine residue in kappa-casein component from bovine mature milk.

This paper describes the glycosylation sites of kappa-casein component P-5 from bovine mature milk. A short glycopeptide was prepared from kappa-casein component P-5 containing two carbohydrate chains by pronase P digestion, followed by gel filtration and ion exchange chromatographies. The glycopeptide obtained corresponded to residues 128-141 (Gly-Glu-Pro-Thr-Ser-Thr-Pro-Thr-Thr-Glu-Ala-Val-Glu-Ser) of kappa-casein A from the results of analyses with chemical and enzymatic procedures. The effect of alkaline borohydride treatment indicated the presence of serine as well as threonine as the binding site of carbohydrate moieties. From the facts of Edman degradation and carboxypeptidase P hydrolysis of glycopeptide treated with alkali, the carbohydrate moieties were considered to be attached to threonine residue No. 133 and serine residue No. 141.