Purification of the major component of the pregnancy-specific beta 1-glycoprotein (SP1) by affinity chromatography, and application to a highly sensitive radioimmunoassay.

The major component of the pregnancy-specific beta 1-glycoprotein (SP1) was purified from pregnancy sera by ammonium sulphate precipitation (1.95 mol/l), anion-exchange chromatography at pH 7.0, positive affinity chromatography, negative affinity chromatography, anion-exchange chromatography at pH 5.0 and, finally, concentration by ultrafiltration or lyophilization. Essentially, the first anion-exchange chromatography separated the major component from three minor components, termed SP1 (gamma), SP1 (alpha 2(2)) and SP1 (alpha 2(1)) on the basis of their electrophoretic mobilities. The yield was 3-6% and the purity about 98-99%. A highly sensitive radioimmunoassay to determine SP1 was developed (detection limit, about 0.5 microgram/l). By using a commercial antiserum against SP1, the slopes of the dose-response curves for purified SP1, a reference preparation from the International Agency for Cancer Research, a commercial SP1 standard, and two of three minor SP1 components were all similar to that of a pool of pregnancy sera, whereas the third minor component, SP1 (gamma), showed a marked difference in slope.