VKORC1 Antibody: Vitamin K epoxide reductase complex subunit 1 (VKORC1) is the enzyme that is responsible for reducing vitamin K 2,3-epoxide to the enzymatically activated form which is essential for blood clotting. This enzymatically activated form of vitamin K is a reduced form required for the carboxylation of glutamic acid residues in some blood-clotting proteins. Fatal bleeding can be caused by vitamin K deficiency and by the vitamin K antagonist warfarin, and it is VKORC1 that is sensitive to warfarin. In humans, mutations in this gene can be associated with deficiencies in vitamin-K-dependent clotting factors and, in humans and rats, with warfarin resistance.