Purification and Characterization of Human Antiplasmin, the Fast-Acting Plasmin Inhibitor in Plasma

Abstract

A simple and rapid purification procedure for antiplasmin is described using affinity chromatography on plasminogen-Sepharose, ion-exchange chromatography on DEAE-Sephadex and chromatography on Concanavalin-A-Sepharose. The final product was shown to be homogeneous using several polyacrylamide gel electrophoretic systems. It is a single-chain glycoprotein with a molecular weight of about 70000 as determined both by dodecyl sulphate/polyacrylamide gel electrophoresis and by sedimentation equilibrium analysis. The sedimentation constant was estimated to be 3.45 S and the carbohydrate content about 14%. Sequence analysis showed the NH2-terminal amino acid sequence to be: Asn-Gln-Glu-Gly-. Immunochemically this protein is different from all the known protease inhibitors in plasma. It was also shown that antiplasmin is a very stable protein if the pH is kept above 6. Antiplasmin rapidly forms a very stable complex with plasmin. Reduction of the complex shows that it is the B-chain of plasmin which is involved. The purified partially reduced and S-carboxy-methylated B-chain of plasmin can also progressively form a complex with antiplasmin. If the reaction between plasmin and antiplasmin is studied in an excess of plasmin a peptide bond seems to be clipped somewhere in the complex between the plasmin B-chain and antiplasmin leading to release of a 14000-Mr fragment (after reduction). This is, however, an event which occurs after complex formation.