Molecular heterogeneity of pregnancy-specific beta 1-glycoprotein (SP1)

Ion-exchange chromatography has been used to isolate three separate forms of Pregnancy-Specific beta 1-Glycoprotein (SP1) from pooled, late-pregnancy human sera. Each of the three components was immunochemically identifiable as SP1, yet distinguishable from each other on the basis of rocket morphology resulting from rocket immunoelectrophoresis (RIE). The elution profile from DEAE Sephacel indicated that each component has an isoelectric point below pH 8.6, but suggested a different charge for each molecular species. Crossed immunoelectrophoresis (XIE) of pooled, late pregnancy serum suggested the presence of each component prior to physico-chemical treatment and showed the components to be characterised by alpha, beta or gamma electrophoretic mobility. The differences in rocket morphology suggested differing affinities for the antiserum, and a difference in molecular size, which was confirmed by gel filtration.