An immunochemical study of proteins with SP₁ determinants in native and acidified pregnancy serum

Summary

The α and ß forms of the pregnancy-associated protein, SP₁, have been studied in late pregnancy serum and in similar serum after acidification. In both sera only two forms of the protein, SP₁α and SP₁ß, could be found; both reacting with antisera against SP₁. On gel chromatography these two forms could be separated, with the intermediate effluent containing a varying mixture of both proteins. Immunoelectrophoresis of the effluent fractions from gel chromatography showed rocket shaped immunoprecipitates whose morphology depended on the mixture of SP₁α and SP₁ß. Crossed immunoelectrophoresis confirmed that only two proteins could be defined with SP₁ antisera; the front running protein having an α₂ electrophoretic mobility and a molecular weight of 430,000, while the slower moving component had the electrophoretic mobility of a ß₁ globulin and a molecular weight of 90,000.