The activation of factor X by hepatocyte plasma membranes.

Synthesis and secretion of blood coagulation factor X was studied during incubations of hepatocytes prepared by perfusion of rat livers with collagenase. The apparent molecular weight of factor X isolated from the incubation medium was about 14,000 less than factor X isolated from rat plasma. The extracellular form of factor X was a two-chain polypeptide and the observed difference in molecular weight was reflected in the heavy chain.

Functional characterization of single-chain factor X from rat liver.

14C-Labeled single-chain factor X prepared by vitamin K-dependent carboxylation in vitro was partially purified by adsorption to BaSO4 and chromatography on DEAE-Sephacel. Known activators of factor X were analyzed for their effect on the single-chain molecule. 14C-Labeled factor X antigens were recovered immunochemically from incubation mixtures and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Vitamin K requirement and the concentration of vitamin K in rat liver.

The concentration of vitamin K was determined in the liver of different strains of rats, and in male and female warfarin-resistant rats by feeding 3H-vitamin K in a purified diet. In each case, the level of vitamin K in the liver correlated approximately with the amount of vitamin K fed. The results indicate that differences in the requirement for vitamin K between the sexes and between strains of rats are due principally to different required concentrations of vitamin K in liver and not to differences in absorption or turnover of the vitamin.