Figure 1
Vitamin K cycle. During vitamin K–dependent carboxylation of glutamic acid to γ-carboxyglutamic acid, the reduced form of vitamin K (KH2) is oxidized to KO by GGCX. KO is reduced to vitamin K by VKOR using the enzyme's 2 active-site cysteine residues. This reaction is sensitive to warfarin inhibition. The reduction of vitamin K to KH2 is carried out in 2 pathways. One pathway is sensitive to warfarin inhibition and also involves 2 free cysteine residues in the enzyme active site (VKOR). The second pathway is resistant to warfarin and uses NAD(P)H as a cofactor.
