Vitamin K2

general structure of vitamin K2 (MK-n)
Vitamin K structures. MK-4 and MK-7 are both subtypes of K2.
Carboxylation reaction – the Vitamin K cycle

One of three types of vitamin K, the other two being vitamin K1 (phylloquinone) and K3 (menadione).

- Vitamin K2

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Vitamin K

Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements.

Vitamin K structures.
Vitamin K1 (phylloquinone) – both forms of the vitamin contain a functional naphthoquinone ring and an aliphatic side chain. Phylloquinone has a phytyl side chain.
Vitamin K2 (menaquinone). In menaquinone, the side chain is composed of a varying number of isoprenoid residues. The most common number of these residues is four, since animal enzymes normally produce menaquinone-4 from plant phylloquinone.
A sample of phytomenadione for injection, also called phylloquinone
Cyclic mechanism of action of vitamin K

Vitamin K includes two natural vitamers: vitamin K1 (phylloquinone) and vitamin K2 (menaquinone).

Menadione

Natural organic compound with the formula C6H42C2H(CH3).

The menadione core is apparent in the structure of vitamin K.

Menadione is converted to vitamin K2 (specifically, MK-4) by the prenyltransferase action of vertebrate UBIAD1.

Electron transport chain

Series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane.

The electron transport chain in the mitochondrion is the site of oxidative phosphorylation in eukaryotes. The NADH and succinate generated in the citric acid cycle are oxidized, which releases the energy of oxygen to power ATP synthase.
Photosynthetic electron transport chain of the thylakoid membrane.
Depiction of ATP synthase, the site of oxidative phosphorylation to generate ATP.

Bacteria use ubiquinone (Coenzyme Q, the same quinone that mitochondria use) and related quinones such as menaquinone (Vitamin K<2).

Bacillus subtilis

Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges.

Gram-stained B. subtilis
Colonies of B. subtilis grown on a culture dish in a molecular biology laboratory.

The fermented beans are recognized for their contribution to a healthy gut flora and vitamin K2 intake; during this long history of widespread use, natto has not been implicated in adverse events potentially attributable to the presence of B. subtilis.

Menatetrenone

Menatetrenone (INN), also known as MK-4, is one of the nine forms of vitamin K2.

Osteoporosis

Systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to bone fragility, and consequent increase in fracture risk.

Elderly woman with osteoporosis showing a curved back from compression fractures of her back bones.
Illustration depicting normal standing posture and osteoporosis
Progression of the shape of vertebral column with age in osteoporosis
Bone density peaks at about 30 years of age. Women lose bone mass more rapidly than men.
The body regulates calcium homeostasis with two pathways; one is signaled to turn on when blood calcium levels drop below normal and one is the pathway that is signaled to turn on when blood calcium levels are elevated.
Osteoporosis locations
Multiple osteoporotic wedge fractures demonstrated on a lateral thoraco-lumbar spine X-ray
Age-standardised hip fracture rates in 2012.
Light micrograph of an osteoclast displaying typical distinguishing characteristics: a large cell with multiple nuclei and a "foamy" cytosol.
Light micrograph of osteoblasts, several displaying a prominent Golgi apparatus, actively synthesizing osteoid containing two osteocytes.
Collapse of vertebra on the right, normal on the left

Vitamin K2 is also used as a means of treatment for osteoporosis and the polymorphisms of GGCX could explain the individual variation in the response to treatment of vitamin K.

Matrix Gla protein

general structure of vitamin K2 (MK-n)

Matrix Gla protein (MGP) is member of a family of vitamin K2 dependent, Gla-containing proteins.

Nitric-oxide reductase

Enzyme, catalyzes the reduction of nitric oxide to nitrous oxide (N2O).

Figure 1. The Nitrogen Cycle. Nitric oxide (NO) and nitrous oxide (N2O) are intermediates in the denitrification of nitrate (NO3−) to nitrogen gas (N2). Nitric oxide reductase reduces NO to N2O.

The catalyzed reaction may be dependent on different participating small molecules: Cytochrome c (EC: 1.7.2.5, Nitric oxide reductase (cytochrome c)), NADPH (EC:1.7.1.14), or Menaquinone (EC:1.7.5.2).

Isochorismate synthase

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Isochorismate synthase EntC, monomer, E.Coli

Isochorismate synthase (EC number 5.4.4.2) is an isomerase enzyme that catalyzes the first step in the biosynthesis of vitamin K2 (menaquinone) in Escherichia coli.

Naphthoate synthase

This is a skeletal structure of the reaction that MenB catalyzes.
3D cartoon representation of the crystal structure of MenB. Each monomer is colored differently.

In enzymology 1,4-dihydroxy-2-naphthoyl-CoA synthase is an enzyme that catalyzes the sixth step in the biosynthesis of phylloquinone and menaquinone, the two forms of vitamin K.