Human placental membrane receptor for IgG. Purification of the receptor and its subunit structure.

The method of purification of the human placental Fc receptor to an active form is described. The FcR was purified from the glycoprotein fraction of the placental membranes by immunoprecipitation and chromatography on DEAE-cellulose. The purified FcR corresponded to 1.5-2% of the protein present in the crude glycoprotein fraction (PGP) and showed the tendency to aggregate. In the presence of 1% SDS, 4 M urea or 5 M guanidine- HCl the placental FcR dissociated into subunits of molecular weight of 60,000-65,000. The 60,000-65,000 dalton glycoprotein subunits regarded as monomers of FcR are composed of two chains of molecular weight 25,000-30,000, linked by disulphide bonds. The subunits, after removal of dissociating agents, displayed IgG binding activity.