About Vitamin K Fat soluble vitamin, Antihemorrhagic. Mechanism of Action of Vitamin K Phytonadione (Vitamin K1) is a synthetic form of vitamin K and is lipid soluble. Vitamin K acts as a cofactor in the synthesis of coagulation proteins- prothrombin, factors VII, IX, and X by liver. Vitamin K dependent changes in the final stage of synthesis of these coagulation proteins is gama-carboxylation of glutamate residues of these zymogen proteins and their descarboxy-forms converted in to active forms- which confers on them the capacity to bind Ca2+ and to get bound to the phospholipid surfaces which are essential properties for participation in the coagulation cascade.