Studies of an inhibitor of the thrombin-fibrinogen reaction localized in rat liver microsomes. Interference with the polymerization step.

A heat-stable, macromolecular inhibitor of the thrombin-fibrinogen reaction localized in rat liver microsomes has been shown to interfere with the polymerization step in the fibrinogen-fibrin conversion. The inhibitor had no effect on thrombin activity as measured with the synthetic, chromogenic substrate BZ-Phe-Val-Arg-pNA. The amount of fibrin formed and the release of fibrinopeptide A were not affected by the inhibitor. Recording of turbidity at 350 nm and 600 nm indicated an inhibition of the lateral aggregation of the end-to-end fibrin polymers. The inhibitor was localized in both the luminal and membrane fractions of the microsomes. The inhibitor activity was not affected by warfarin treatment of the rats.