Vitamin K epoxide reductase (VKOR) recycles reduced vitamin K, which is used subsequently as a co-factor in the gamma-carboxylation of glutamic acid residues in blood coagulation enzymes. VKORC1 is a member of a large family of predicted enzymes that are present in vertebrates, Drosophila, plants, bacteria and archaea [1]. Four cysteine residues and one residue, which is either serine or threonine, are identified as likely active-site residues [1]. In some plant and bacterial homologues the VKORC1 homologous domain is fused with domains of the thioredoxin family of oxidoreductases [1].

1: Vitamin K epoxide reductase: homology, active site and catalytic mechanism. Goodstadt L, Ponting CP; Trends Biochem Sci 2004;29:289-292. PMID:15276181