Summary
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.
