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Phosphorylation, glycosylation and amino acid sequence of component PP3 from the proteose peptone fraction of bovine milk

1993; Cambridge University Press; Volume: 60; Issue: 4 Linguagem: Inglês

10.1017/s0022029900027886

1469-7629

Esben S. Sørensen, Torben E. Petersen,

Digestive system and related health

Summary Component PP3 is a phosphorylated glycoprotein with an apparent molecular mass of 28 kDa isolated from the proteose peptone fraction of bovine milk. The function of the protein is not known. The primary structure has been determined and shown to contain 135 amino acid residues (EMBL accession no. P80195). It was phosphorylated at Ser 29 , Ser 34 , Ser 38 , Ser 40 and Ser 46 . Two O-linked carbohydrate groups were found at Thr 16 and Thr 86 , while one N-linked carbohydrate group was present at Asn 77 . Thr 16 was only ∼ 50% glycosylated. The amino sugar detected by the amino acid analyser at Thr 86 was mainly galactosamine but a small amount of glucosamine was also present. The amino sugars found in the carbohydrate group linked to Asn 77 were both glucosamine and galactosamine. A fragment of PP3 has been isolated from milk and shown to correspond to residues 54–135. This fragment was probably generated by plasmin hydrolysing the Arg 53 –Ser 54 bond.