Isolation and some characteristics of urokinase inhibitors isolated from pig leucocytes

Two inhibitors of urokinase were isolated from the extracts of the nuclei of peripheral pig leucocytes, by ion exchange chromatography and by gel filtration on Sephadex G-100 and G-150. Only the inhibitor with the higher molecular weight was isolated in the homogenous form, in a single polypeptide chain with molecular weight of 68,000, designated Inhibitor-3. This inhibitor has an isoelectric point from 4.4 to 4.5 and is stable in buffer solutions from pH 3 to 8, and belongs to the type of so-called fast reacting inhibitors.