Protein C inhibitor: purification and proteinase reactivity.

Protein C inhibitor was purified from human plasma by a modification of a published procedure (Suzuki, K., Nishioka, J., and Hashimoto, S. J. Biol. Chem. 258, 163-168, 1983). Approximately 1 mg of pure protein was obtained from 1 L plasma, a yield of about 17%. The protein C inhibitor preparation did not lose activity over 4 weeks at 4 degrees C. Second order rate constants were measured for the inhibition of activated protein C, thrombin, and urokinase, and bimolecular complexes of protein C inhibitor with activated protein C and thrombin were visualized by denaturing polyacrylamide gel electrophoresis. Heparin accelerated the inhibition of the three proteinases in a manner consistent with a template mechanism. Plasma or pure protein C inhibitor (at the same concentration) showed the same effect of heparin on activated protein C inhibition, indicating that protein C inhibitor accounts for all the heparin-dependent inhibition of activated protein C in vivo.