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.