Immunological observations on the relationship of SP 1 alpha to SP 1 beta

Distribution of SP1, immunoreactivity among different plasma proteins: real molecular heterogeneity or adsorption of SP1-beta to other plasma proteins?

Three SP1-containing factors from pooled term pregnancy sera were subjected to crossed immunoelectrophoresis. New patterns as far as electrophoretic mobilities and shapes of the immunoprecipitates were revealed. The appearance of an additional anodic radioimmunoassayable activity in agarose electrophoresis of mixed SP1-alpha and SP1-beta suggested a binding capacity of SP1-alpha for SP1-beta determinants. In the serum of a single patient at the third trimester of pregnancy we also found two SP1 variants, possessing little radioimmunological reactivity and with crossed immunoelectrophoretic characteristics quite different from those of the 'usual' alpha and beta SP1 forms. These results suggest that, in this particular case, the overall SP1 production cannot be evaluated by competitive binding assay and, that in general, SP1 is a complex antigen the heterogeneity of which can be determined following adsorption of some beta epitopes to another serum protein.

Studies on the half-life of Schwangerschaftsprotein 1 (SP1)

Schwangerschaftsprotein 1 (SP1) was measured in 10 women at intervals after delivery of the placenta. SP1 alpha decreased more sharply than SP1 beta and showed evidence of a two-compartmental distribution in the mother. Trace amounts of both proteins could still be detected 5 weeks after delivery. It is concluded that the findings support the view that the two proteins are separate biological entities and that there is a possibility that SP1 beta is generated from SP1 alpha in the maternal compartment.