The purification and properties of cancer procoagulant from murine tumors.

The protease, cancer procoagulant, was isolated from three murine metastatic tumors and was purified to apparent homogeneity (SDS-PAGE) from Lewis lung cells by the sequence of (NH4)2SO4 precipitation, DE-53 anion-exchange chromatography, and Sephacryl 200 chromatography. The murine tumor enzyme has a molecular weight of 68,000 and Ca2+ is required for procoagulant and proteolytic activity; thus, the murine enzyme is very similar to that isolated from rabbit tumors. Two peptidyl chromogenic substrates of cancer procoagulant were discovered, facilitating kinetic and inhibition studies with the enzyme. The peptide substrate structures and the results of inhibition studies suggest that cancer procoagulant is thrombin-like in specificity but is a thiol protease.