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== Introduction ==

Vitamin K epoxide reductase (VKOR) is the enzyme responsible for regenerating vitamin K from vitamin K epoxide to support blood coagulation.

[[Image:Vitamin_K_Cycle_IJEV.jpg|300 px|left|thumb|Figure 1. Vitamin K Cycle]]

[[Image:barrel_domain_smaller.jpg|200 px|right|thumb|Figure 2. VKOR with Barrel Domain]]

=== Vitamin K Cycle ===

Vitamin K is essential for blood clotting in the body. The fully reduced form, KH2, allows the gamma carboxylation of blood clotting cofactors and is turned into the epoxide form in the process. Vitamin K epoxide reductase turns the epoxide back to the fully reduced form so the reduced form can be used again. This transformation happens in two steps including converting the epoxide to partially oxidized Vitamin K then converting the partially oxidized Vitamin K to the fully reduced hydroquinone. <ref name="Stafford">PMID:16102054</ref>

=== Structural Overview ===

VKOR consists of four <scene name='90/904330/Transmembrane_helices/1'>transmembrane helices</scene> embedded in the endoplasmic reticulum membrane. The files on the RCSB Protein Data Bank include a barrel domain that is not pertinent to the function of VKOR. The images presented here have been edited to remove the barrel domain and renumbered to correspond with the article by Liu. <ref name="Liu">PMID:33154105</ref>. The original image with the barrel domain in context is shown in Figure 2. Helices one and two are connected by the beta hairpin region which contains two of the active cysteines, C43 and C51. VKOR also has a cap domain covering the active site, made up of an anchor, loop, and helix.

=== Function ===

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@@ Line 5: / Line 5: @@
 == Introduction ==
 Vitamin K epoxide reductase (VKOR) is the enzyme responsible for regenerating vitamin K from vitamin K epoxide to support blood coagulation.
+[[Image:Vitamin_K_Cycle_IJEV.jpg|300 px|left|thumb|Figure 1. Vitamin K Cycle]]
+[[Image:barrel_domain_smaller.jpg|200 px|right|thumb|Figure 2. VKOR with Barrel Domain]]
 === Vitamin K Cycle ===
 Vitamin K is essential for blood clotting in the body. The fully reduced form, KH2, allows the gamma carboxylation of blood clotting cofactors and is turned into the epoxide form in the process. Vitamin K epoxide reductase turns the epoxide back to the fully reduced form so the reduced form can be used again. This transformation happens in two steps including converting the epoxide to partially oxidized Vitamin K then converting the partially oxidized Vitamin K to the fully reduced hydroquinone. <ref name="Stafford">PMID:16102054</ref>
 === Structural Overview ===
+VKOR consists of four <scene name='90/904330/Transmembrane_helices/1'>transmembrane helices</scene> embedded in the endoplasmic reticulum membrane. The files on the RCSB Protein Data Bank include a barrel domain that is not pertinent to the function of VKOR. The images presented here have been edited to remove the barrel domain and renumbered to correspond with the article by Liu. <ref name="Liu">PMID:33154105</ref>. The original image with the barrel domain in context is shown in Figure 2.  Helices one and two are connected by the beta hairpin region which contains two of the active cysteines, C43 and C51. VKOR also has a cap domain covering the active site, made up of an anchor, loop, and helix.
 === Function ===