Sørensen E S, Petersen T E
Department of Molecular Biology, University of Aarhus, Denmark.
J Dairy Res. 1993 Nov;60(4):535-42. doi: 10.1017/s0022029900027886.
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 Ser29, Ser34, Ser38, Ser40 and Ser46. Two O-linked carbohydrate groups were found at Thr16 and Thr86, while one N-linked carbohydrate group was present at Asn77. Thr16 was only approximately 50% glycosylated. The amino sugar detected by the amino acid analyser at Thr86 was mainly galactosamine but a small amount of glucosamine was also present. The amino sugars found in the carbohydrate group linked to Asn77 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 Arg53-Ser54 bond.
组分PP3是一种磷酸化糖蛋白，表观分子量为28 kDa，从牛乳的蛋白胨部分分离得到。该蛋白的功能尚不清楚。其一级结构已被确定，包含135个氨基酸残基（EMBL登录号：P80195）。它在Ser29、Ser34、Ser38、Ser40和Ser46处被磷酸化。在Thr16和Thr86处发现两个O-连接的碳水化合物基团，而在Asn77处存在一个N-连接的碳水化合物基团。Thr16仅约50%被糖基化。氨基酸分析仪在Thr86处检测到的氨基糖主要是半乳糖胺，但也存在少量葡萄糖胺。与Asn77连接的碳水化合物基团中发现的氨基糖既有葡萄糖胺也有半乳糖胺。PP3的一个片段已从牛奶中分离出来，显示对应于54 - 135位残基。该片段可能是由纤溶酶水解Arg53 - Ser54键产生的。
