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A physiologically inactive prothrombin protein has been purified from the plasma of dicumarol-treated cows to a high level of purity.This protein gave 80% as much precipitation in an assay against bovine prothrombin antibody as did normal bovine prothrombin.This could be due to a difference in antigenicity, or it could be a reflection of nonhomogeneity of the preparation.It was very similar to normal prothrombin in its carbohydrate and amino acid composition, its ability to be activated by several nonphysiological prothrombin activators, and its molecular weight as judged by gel electrophoresis.Its disc gel electrophoretic pattern also showed little difference from that of normal prothrombin unless calcium was included in the gel buffers.Under these conditions it was apparent that the inactive prothrombin did not bind calcium to the same degree as the normal prothrombin.The other significant differences between these two proteins are their physiological activity and their adsorption onto barium citrate precipitates.In every case the abnormal prothrombin failed to have these properties.It appears that these three differences are due to the same property of prothrombin and that this is a result of vitamin K action.That is, vitamin K action is required in the metabolic step which is needed to produce the calcium-binding sites, and these are necessary for physiological activity and are responsible for barium citrate adsorption.These data suggest that vitamin K acts by chemically altering prothrombin in some unknown fashion, or in the attachment of a previously unrecognized prosthetic group.There is considerable evidence that the selective control which is exerted by vitamin K on the biosynthesis of the blood-clotting
Nelsestuen et al. (Fri,) studied this question.