Investigations into the molecular heterogeneity of pregnancy-specific beta 1-glycoprotein (SP1)

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.

Pregnancy specific beta 1-glycoprotein (SP1) conversion of SP1 beta to SP1 alpha by "acidification": an artefact

Late pregnancy serum and plasma were examined in rocket immunoelectrophoresis (RIE) and crossed immunoelectrophoresis (XIE) before and after "acid treatment" (pH 2.5, 10 min). The analysis revealed changes in the precipitation morphology in the majority of circulating proteins extending from the albumin to the gamma-region. In RIE, the precipitation pattern of SP1 was altered, this change being independent of polyethylene glycol. In addition, XIE analysis of SP1 revealed a change in the precipitation morphology with no change in electrophoretic mobility. The results can be explained by non-specific aggregation and denaturation due to "acid treatment", and are therefore unlikely to be of any biological or immunochemical importance.