Pregnancy-associated plasma protein A interaction with heparin: a critical appraisal

Positive affinity chromatography on heparin-Sepharose has proved a most crucial step in the purification of pregnancy-associated plasma protein A (PAPP-A). In this chromatographic procedure, PAPP-A was purified almost 500-fold from term pregnancy serum. Further purification was achieved by gel filtration and negative immunoaffinity chromatography. Both PAPP-A and free heparin inhibited granulocyte elastase (HGE) activity. Whereas free heparin inhibited only in hypotonic buffers, PAPP-A inhibited HGE in hypertonic buffers also. However, PAPP-A did not inhibit other proteases (trypsin, chymotrypsin, plasmin, fibroblast collagenase) or proteolytic cascades (complement activation). Since heparin was not detected in the purified PAPP-A, the inhibition of HGE was not due to desorbed or leeched heparin ligand.