Vitamin K is a family of structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation or for controlling binding of calcium in bones and other tissues. The complete synthesis involves final modification of these so-called "Gla proteins" by the enzyme gamma-glutamyl carboxylase that uses vitamin K as a cofactor.
Protein disulfide isomerase, or PDI, is an enzyme in the endoplasmic reticulum (ER) in eukaryotes and the periplasm of bacteria that catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. This allows proteins to quickly find the correct arrangement of disulfide bonds in their fully folded state, and therefore the enzyme acts to catalyze protein folding.
Methionine synthase (MS, MeSe, MTR) is responsible for the regeneration of methionine from homocysteine. In humans it is encoded by the MTR gene (5-methyltetrahydrofolate-homocysteine methyltransferase). Methionine synthase forms part of the S-adenosylmethionine (SAMe) biosynthesis and regeneration cycle, and is the enzyme responsible for linking the cycle to one-carbon metabolism via the folate cycle. There are two primary forms of this enzyme, the Vitamin B12 (cobalamin)-dependent (MetH) and independent (MetE) forms, although minimal core methionine synthases that do not fit cleanly into either category have also been described in some anaerobic bacteria. The two dominant forms of the enzymes appear to be evolutionary independent and rely on considerably different chemical mechanisms. Mammals and other higher eukaryotes express only the cobalamin-dependent form. In contrast, the distribution of the two forms in Archaeplastida (plants and algae) is more complex. Plants exclusively possess the cobalamin-independent form, while algae have either one of the two, depending on species. Many different microorganisms express both the cobalamin-dependent and cobalamin-independent forms.
Glutathione reductase (GR) also known as glutathione-disulfide reductase (GSR) is an enzyme that in humans is encoded by the GSR gene. Glutathione reductase catalyzes the reduction of glutathione disulfide (GSSG) to the sulfhydryl form glutathione (GSH), which is a critical molecule in resisting oxidative stress and maintaining the reducing environment of the cell. Glutathione reductase functions as dimeric disulfide oxidoreductase and utilizes an FAD prosthetic group and NADPH to reduce one molar equivalent of GSSG to two molar equivalents of GSH:
Dicoumarol (INN) or dicumarol (USAN) is a naturally occurring anticoagulant drug that depletes stores of vitamin K. It is also used in biochemical experiments as an inhibitor of reductases.
Vitamin K epoxide reductase (VKOR) is an enzyme that reduces vitamin K after it has been oxidised in the carboxylation of glutamic acid residues in blood coagulation enzymes. VKOR is a member of a large family of predicted enzymes that are present in vertebrates, Drosophila, plants, bacteria and archaea. In some plant and bacterial homologues, the VKOR domain is fused with domains of the thioredoxin family of oxidoreductases.
Gamma-glutamyl carboxylase is an enzyme that in humans is encoded by the GGCX gene, located on chromosome 2 at 2p12.
In enzymology, a 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase (EC 1.3.1.28) is an enzyme that catalyzes the chemical reaction
In enzymology, a vitamin-K-epoxide reductase (warfarin-insensitive) is an enzyme that catalyzes the chemical reaction
[Methionine synthase] reductase, or Methionine synthase reductase, encoded by the gene MTRR, is an enzyme that is responsible for the reduction of methionine synthase inside human body. This enzyme is crucial for maintaining the one carbon metabolism, specifically the folate cycle. The enzyme employs one coenzyme, flavoprotein.
In enzymology, a CoA-disulfide reductase (EC 1.8.1.14) is an enzyme that catalyzes the chemical reaction
Flavin reductase a class of enzymes. There are a variety of flavin reductases, which bind free flavins and through hydrogen bonding, catalyze the reduction of these molecules to a reduced flavin. Riboflavin, or vitamin B, and flavin mononucleotide are two of the most well known flavins in the body and are used in a variety of processes which include metabolism of fat and ketones and the reduction of methemoglobin in erythrocytes. Flavin reductases are similar and often confused for ferric reductases because of their similar catalytic mechanism and structures.
In enzymology, a L-methionine (S)-S-oxide reductase (EC 1.8.4.13) is an enzyme that catalyzes the chemical reaction
In enzymology, a NAD(P)H dehydrogenase (quinone) (EC 1.6.5.2) is an enzyme that catalyzes the chemical reaction
Sulfite reductases (EC 1.8.99.1) are enzymes that participate in sulfur metabolism. They catalyze the reduction of sulfite to hydrogen sulfide and water. Electrons for the reaction are provided by a dissociable molecule of either NADPH, bound flavins, or ferredoxins.
The human gene VKORC1 encodes for the enzyme, Vitamin K epOxide Reductase Complex (VKORC) subunit 1. This enzymatic protein complex is responsible for reducing vitamin K 2,3-epoxide to its active form, which is important for effective clotting (coagulation). In humans, mutations in this gene can be associated with deficiencies in vitamin-K-dependent clotting factors.
Ferredoxin-thioredoxin reductase EC 1.8.7.2, systematic name ferredoxin:thioredoxin disulfide oxidoreductase, is a [4Fe-4S] protein that plays an important role in the ferredoxin/thioredoxin regulatory chain. It catalyzes the following reaction:
1,4-Naphthoquinone or para-naphthoquinone is a quinone derived from naphthalene. It forms volatile yellow triclinic crystals and has a sharp odor similar to benzoquinone. It is almost insoluble in cold water, slightly soluble in petroleum ether, and more soluble in polar organic solvents. In alkaline solutions it produces a reddish-brown color. Vitamin K is a derivative of 1,4-naphthoquinone. It is a planar molecule with one aromatic ring fused to a quinone subunit. It is an isomer of 1,2-naphthoquinone.
Methionine-S-oxide reductase (EC 1.8.4.5, methyl sulfoxide reductase I and II, acetylmethionine sulfoxide reductase, methionine sulfoxide reductase, L-methionine:oxidized-thioredoxin S-oxidoreductase) is an enzyme with systematic name L-methionine:thioredoxin-disulfide S-oxidoreductase. This enzyme catalyses the following chemical reaction
Peptidyl-glutamate 4-carboxylase (EC 4.1.1.90, vitamin K-dependent carboxylase, gamma-glutamyl carboxylase) is an enzyme with systematic name peptidyl-glutamate 4-carboxylase (2-methyl-3-phytyl-1,4-naphthoquinone-epoxidizing). This enzyme catalyses the following chemical reaction
