Immunoadsorbent isolation of pregnancy-specific beta 1-glycoprotein from maternal serum

A three-step procedure for the purification of pregnancy-specific beta 1-glycoprotein (PS beta 1G) on a milligram scale from maternal serum has been developed. The principal purification was achieved by the use of an immunoadsorbent and the remaining impurities were removed by hydroxylapatite chromatography and negative affinity chromatography. The overall procedure resulted in the purification of approximately 10 mg of PS beta 1G which represented about 21% of PS beta 1G in 300 mL, of serum. The PS beta 1G was of high purity as shown by analytical polyacrylamide gel electrophoresis, sodium dodecyl sulfate--polyacrylamide gel electrophoresis, and immunochemical tests. Experiments by immunoelectrophoresis and gel chromatography indicate that the electrophoretic mobility and relative mass of the purified PS beta 1G are very similar to those of the native serum protein. Structural analysis of PS beta 1G suggests that it is composed of two identical subunit chains bonded noncovalently. However, a trimeric structure for PS beta 1G cannot be ruled out based on the uncertainty of relative mass estimates by gel chromatography in nondenaturing solvent. The anomalous characteristics of a previous purified polymeric form of PS beta 1G (PS beta 1G-I) are discussed in relation to the new findings presented here.