Kobayashi K, Mafune N, Narimatsu H, Nakao H, Taniguchi N
Department of Pediatrics, Hokkaido University School of Medicine, Sapporo, Japan.
Immunol Lett. 1996 Apr;50(1-2):99-104. doi: 10.1016/0165-2478(96)02528-x.
Secretory component (SC) in external secretions is a soluble form of the polymeric immunoglobulin-receptor that is expressed on the cell membrane of mucosal epithelial cells. beta-(1-4)galactosyl transferase (beta-GT) is an enzyme that transfers galactose to non-reducing N-acetylglucosamine residues on various glycoproteins and is present in a soluble form in secretions as well as in a membrane-bound form. beta-GT is considered to have affinity for glycoproteins, including IgA in secretion. It has been claimed that these two proteins are related to or identical with each other. In the present study, we defined that the SC and the beta-GT are each independent molecules by the following facts; (1) both molecules are separable either by antibody-affinity chromatography, conventional ion-exchange or molecular exclusion chromatography, (2) conventionally purified SC from human milk contained neither enzymatic activity or antigenic determinants of the beta-GT, (3) recombinant beta-GT does not show reactivity with antibodies to SC, and (4) the SC showed no reactivity with antibody to beta-GT.
外分泌液中的分泌成分（SC）是多聚免疫球蛋白受体的一种可溶性形式，在黏膜上皮细胞的细胞膜上表达。β-（1-4）半乳糖基转移酶（β-GT）是一种将半乳糖转移至各种糖蛋白上非还原性N-乙酰葡糖胺残基的酶，它以可溶性形式存在于分泌物中，也以膜结合形式存在。β-GT被认为对包括分泌型IgA在内的糖蛋白具有亲和力。据称这两种蛋白相互关联或相同。在本研究中，我们通过以下事实确定SC和β-GT均为独立分子：（1）这两种分子均可通过抗体亲和色谱法、常规离子交换色谱法或分子排阻色谱法分离；（2）从人乳中常规纯化得到的SC既不含有β-GT的酶活性，也不含有其抗原决定簇；（3）重组β-GT不与抗SC抗体发生反应；（4）SC不与抗β-GT抗体发生反应。
