Heterogeneity of the pregnancy-specific beta 1-glycoprotein (SP1)

The pregnancy-specific beta 1-glycoprotein (SP1) in pregnant serum fractionated by ammonium sulfate precipitation and anion exchange chromatography was investigated by various electrophoretic methods. From these investigations it appears that in addition to the major component SP1(beta) three other components are present, termed SP1(gamma), SP1 (alpha 2(2)) and SP1 (alpha 2(1) on the basis of their electrophoretic mobilities. The isoelectric point (pI), estimated by isoelectric focusing, and the relative molecular mass (Mr), estimated by Sephadex G-200 gel filtration chromatography are for SP1(gamma): pI 2.9--4.9, Mr approximately 80000; SP1(beta): pI 2.5--4.5, Mr approximately 80000; SP1(alpha 2(2)): pI less than or equal to 6, Mr greater than or equal to 200000; SP1(alpha 2(1)): pI less than 3, Mr approximately 30000. Based on the interaction with phenyl-Sepharose and concanavalin A all four species of SP1 are amphiphilic glycoproteins.