SECRETORY COMPONENT, THE RECEPTOR FOR POLYMERIC IMMUNOGLOBULIN, HAS NOTHING TO DO WITH BETA-GALACTOSYLTRANSFERASE IN HUMAN-MILK

Secretory component (SC) in external secretions is a soluble form of t he polymeric immunoglobulin-receptor that ia expressed on the cell mem brane of mucosal epithelial cells. beta-(l-l)galactosyl transferase (b eta-GT) is an enzyme that transfers galactose to non-reducing N-acetyl glucosamine residues on various glycoproteins and is present in a solu ble form in secretions as well as in a membrane-bound form. beta-GT is considered to have affinity for glycoproteins, including IgA in secre tion. It has been claimed that these two proteins are related to or id entical 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 chromato graphy, conventional ion-exchange or molecular exclusion chromatograph y, (2) conventionally purified SC from human milk contained neither en zymatic activity or antigenic determinants of the beta-GT, (3) recombi nant beta-GT does not show reactivity with antibodies to SC and (4) th e SC showed no reactivity with antibody to beta-GT.