Molecular weight of undegraded plasma factor V

The molecular size and immunochemical properties of the unfractionated factor V present in plasma collected by venipuncture into a broad-spectrum anticoagulant and platelet-inhibited mixture were compared with those reported for the isolated, single-chain factor V molecular of 330 000 daltons. The anticoagulant--plasma mixture included 0.28% trisodium citrate, 2 mM benzamidine hydrochloride, 0.02% soybean trypsin inhibitor, 2.0 mM diisopropyl phosphorofluoridate, 10 microM dansylarginine N-(3-ethyl-1,5-pentanediyl)amide, and 5 microM prostaglandin E1. The Stokes radius of unfractionated factor V present in highly inhibited plasma (93 A) is virtually identical with the Stokes radius predicted from the hydrodynamic data for the highly asymmetric, single-chain factor V molecule (91 A). With an expression which relates the Stokes radius and the sedimentation coefficient to the molecular weight of hydrodynamic units, the molecular weight obtained for factor V, using gel filtration data, is 336 000, in good agreement with the molecular weight determined from the sedimentation equilibrium, 330 000. In contrast, the Stokes radius for the factor Va present in serum is significantly smaller (50.5 A) and equivalent to the Stokes radius obtained upon activation of isolated factor V with thrombin. Immunochemical comparisons of the factor V present in the inhibited plasma and isolated factor V were conducted by using burro antibovine factor V antibody and the technique of immunoelectrophoresis. The factor V antigen present in both sources is immunochemically identical, as is the electrophoretic mobility of both factor V preparations. These data serve to justify the conclusion that the factor V isolated as a single-chain 330 000-dalton molecule corresponds to the factor V circulating in plasma.