Summary
Procedures for the separation of two inhibitors of the activation of plasminogen to
plasmin by urokinase are described. Tissue thromboplastin was removed by adsorption
to Al(0H)3 gel followed by ultracentrifugation. Plasminogen, plasminogen activator, a coagulation
inhibitor and hemoglobin were removed by ion exchange chromatography (CM- or DEAE-Sephadex
with NaCl gradients). The minor UK inhibitor is a relative basic protein with a pI
of about 5.8. The major inhibitor was purified further by isoelectric focusing, preparative
electrophoresis in polyacrylamide gel, and gel filtration. This inhibitor has α1-motility, the pI is about 5.2, and the molecular weight about 100,000. It inactivates
urokinase progressively, but does not inhibit streptokinase, plasmin or thrombin.