Purification and some properties of rat alpha 2-plasmin inhibitor.

alpha 2-Plasmin inhibitor was purified from rat plasma by the procedures including sequential lysine-Sepharose chromatography, ammonium sulfate precipitation and plasminogen-Sepharose, DEAE-Sephadex, concanavalin A-Sepharose, and Sephadex G-200 chromatographies. The final preparation was homogeneous as judged by sodium dodecyl sulfate polyacrylamide gel- and immuno-electrophoresis. It was a single polypeptide chain with a molecular weight of about 7.1 X 10(4) daltons and was found to possess fast-acting antiplasmin activity. There existed other molecular forms of alpha 2-plasmin inhibitor-related antigen with molecular weight of 6.3 X 10(4) and 6.1 X 10(4) daltons. The latter was found to be inactive in binding to plasminogen and in inhibiting plasmin activity. Normal plasma level of alpha 2-plasmin inhibitor in rats was immunologically determined to be 7.9 +/- 0.8 mg/dl. Indirect evidence was obtained that rat alpha 2-plasmin inhibitor was incorporated into cross-linked fibrin during blood clotting.