Characterization of four human pregnancy-associated plasma proteins

Abstract

Four proteins have been detected in third-trimester human pregnancy plasma by gel immunodiffusion methods, using antisera to pregnancy plasma that had been exhaustively absorbed with nonpregnancy plasma. These antisera failed to react with plasma from untreated normal nonpregnant females or from males. Two of the pregnancy-associated plasma proteins (PAPP-B and PAPP-C) migrated as β-globulins and the other two (PAPP-A and PAPP-D) as α2-globulins in immunoelectrophoresis. PAPP-B was regularly detected only by crossed-immunoelectrophoresis with the reagents available and it was not further studied here. Proteinases destroyed the immunologic reactivities of PAPP-A, C, and D, but none of them was inactivated by ribonuclease and deoxyribonuclease, and they did not appear to contain lipids. They were all stable to heat at 60° C. for 30 minutes, but were variably labile at higher temperatures. The three PAPP's also showed varying lability at pH extremes. They were well separated from each other in gel filtration on Sephadex G-200 and Sepharose 6B, in DEAE-cellulose column chromatography, and in sucrose density gradient ultracentrifugation, but not by step-wise salting out precipitation or gradient solubilization with ammonium sulfate. Molecular weights estimated by gel filtration were found to be 750,000 for PAPP-A, 110,000 for PAPP-C, and 20,000 for PAPP-D. Their isoelectric points were found by isoelectric focusing in ampholine-sucrose gradients: PAPP-A, pH 4.4; PAPP-C, pH 3.8; PAPP-D, pH 5.7. PAPP-C contained iron detectable by histochemical staining methods; it was heterogeneous and had minor components of different charge and isoelectric point (pH 6.0).