Menaquinone (Vitamin K2)
Vitamin K is found in plants as phylloquinone (vitamin K1) and in animals as menaquinone (vitamin K2).
Vitamin K2 is essential for the carboxylation of glutamate residues in certain proteins, to give -carboxyglutamate. This modification allows the protein to bind calcium, an essential event in the blood clotting cascade. Carboxylation of glutamate is also important in other proteins involved in the mobilization or transport of calcium.
Vitamin K exists in two forms, K1 and K2. Both vitamins are coenzymes of gammaglutamyl carboxylase and are thus able to regulate mineralization of bone and calcification of blood vessels. Vitamin K2 however is more effective than vitamin K1 with respect to osteoclastogenesis likewise hypocholesterolemic effects and the ability to slow atherosclerotic progression have only been observed with vitamin K2. This may be due in part to the geranylgeranyl side chain of vitamin K2 which is thought to inhibit the mevalonate pathway, thus preventing the prenylation of growth factors required for osteoclast activation in much the same way as nitrogen-containing bisphosphonates. This therefore suggests that modelling of vitamin K2 may lead to the development of therapeutic candidates able to reduce resorption, increase bone mineralization and limit atherosclerosis. Furthermore, targeting vitamin K2 over vitamin K1 may be confer beneficial pharmacokinetics given that vitamin K1 concentrates in the liver while vitamin K2 is well distributed to bone and blood vessel walls. Equally, this profile is expected to limit the primary adverse effect associated with vitamin K, negative interactions with coumarin anti-coagulants, since the proteins involved in coagulation are primarily synthesized in the liver.
Vitamin K2 is the collective term for a group of vitamin K compounds called menaquinones. The menaquinone homolgues are characterized by the number of isoprene residues comprising the side chain. The side chain is located at position 3 of the naphthoquinone ring. The group chemical name of the menaquinones is 2-methyl-3-all-trans-polyprenyl-1, 4-naphthoquinones. Menaquinones with side chains of up to 15 isoprene units have been described. Menaquinones of from two to 13 isoprene units have been found in human and animal tissues. Menaquinones are designated by the name menaquinone followed by a number. The number refers to the number of isoprene residues in the structure. Thus, menaquinone-4, abbreviated MK-4, possesses four isoprene residues in the side chain. Menaquinone-7 possesses seven isoprene units in the side chain. The menaquinones may also be designated by the number of carbons in the side chain. An isoprene residue contains five carbons. Thus, menaquinone-4 is also called vitamin K2 (20) and menaquinone-7 is also called vitamin K2 (35). Menaquinone-4 is also known as menatetrenone. The fermented soybean product natto is rich in menaquinone-7. Menaquinone-4 is the predominant form of vitamin K in the rat brain.
CAS No.: 863-61-6