Open AccessPlacental alkaline phosphatase has a binding site for the human immunoglobulin‐G Fc portion
Author(s) -
MAKIYA Ricardo,
STIGBRAND Torgny
Publication year - 1992
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1992.tb16785.x
Subject(s) - placental alkaline phosphatase , syncytiotrophoblast , alkaline phosphatase , microbiology and biotechnology , placenta , affinity chromatography , dissociation constant , antibody , fragment crystallizable region , biochemistry , receptor , phosphatase , immunoglobulin g , chemistry , biology , protein subunit , enzyme , immunology , fetus , pregnancy , gene , genetics
Affinity chromatography of human plasma on placental‐alkaline‐phosphatase–Sepharose columns (placental alkaline phosphatase, PLAP) yielded consistently a pure protein which was identified as IgG on the basis of electrophoretical and immunological comparisons with authentic human IgG. SDS/PAGE of the protein revealed, under reducing conditions, two polypeptides of 55 kDa and 25 kDa. The N‐terminal amino acid sequence (12 residues) of the 55‐kDa subunit presented high similarity (83–100%) with known sequences of immunoglobulin gamma chains. The IgG binds by its Fc portion to a fully exposed domain in the plasma‐membrane‐anchored PLAP. Scatchard analysis of the interaction gave a dissociation constant of 3.68 γM, a value close to those found for haematopoietic cells and syncytiotrophoblast Fc receptors. The latter was affinity purified from human placenta as the major IgG‐binding component and presented cross‐immunoreactivity with anti‐PLAP antibodies, indicating that PLAP and the putative placental Fc receptor could be identical molecules.