Vitamin menaquinone

Meganathan, R., Biosynthesis of menaquinone (vitamin Kj) and ubiquinone (coenzyme Q) a perspective on enzymatic mechanism. Vitamins Hormones, 61, 173, 2001. 

Isoprene chains are sometimes used as lipid anchors to fix molecules to membranes (see p. 214). Chlorophyll has a phytyl residue (1 = 4) as a lipid anchor. Coenzymes with isoprenoid anchors of various lengths include ubiquinone (coenzyme Q 1 = 6-10), plastoqui-none (1 = 9), and menaquinone (vitamin K 1 = 4-6). Proteins can also be anchored to membranes by isoprenylation. 

Vitamin K activity is associated with several quinones, including phylloquinone (vitamin Kj), menadione (vitamin K3), and a variety of menaquinones (vitamin K2). These quinones promote the synthesis of proteins that are involved in the coagulation of blood. These proteins include prothrombin, factor VII (proconvertin), factor IX (plasma thromboplastin), and factor X (Stuart factor). A detailed discussion of blood coagulation is found in Chapter 22. The vitamin K quinones are obtained from three major sources. Vitamin K is present in vari-... 

The structure of vitamin K is characterized by methylnaphthoquinone rings with a side chain at position 3. It exists naturally in two forms phylloquinone (vitamin Kt 6.13) occurs only in plants, while menaquinones (vitamin K2 6.14) are a family of compounds with a side chain consisting of between 1 and 14 isoprene units. Menaquinones are synthesized only by bacteria (which inhabit the human gastrointestinal tract and thus provide some of the vitamin K required by the body). Menadione (vitamin K3 6.15) is a synthetic compound with vitamin K activity. Unlike Kj and K2, menadione is water soluble and is not active until it is alkylated in vivo. 

Menaquinones (vitamin K2) 818, 821 Mengo virus 247 Menkes disease 883 Mercaptans 624 Mercaptides 550 Mercaptoethanol 98... 

Two forms of vitamin K exist in nature. Phylloquinone (vitamin K,) is a specific vitamer synthesized by green plants in the chloroplasts menaquinones (vitamin K2) are a series of structural analogs that are synthesized by bacteria. 

Reaction centers of purple bacteria typically contain three polypeptides, four molecules of bacteriochlorophyll, two bacteriopheophytins, two quinones, and one nonheme iron atom. In some bacterial species, both quinones are ubiquinone. In others, one of the quinones is menaquinone (vitamin K2), a naphthoquinone that resembles ubiquinone in having a long side chain (fig. 15.10). Reaction centers of some species, such as Rhodopseudomonas viridis, also have a cytochrome subunit with four c-type hemes. 

The structures of ubiquinone, menaquinone (vitamin K2), plastoquinone, and phylloquinone (vitamin K ). Purple photosynthetic bacteria contain ubiquinone, menaquinone, or both, depending on the bacterial species chloroplasts contain plastoquinone and phylloquinone. 

Many patients with these conditions may also be prescribed warfarin. Coenzyme Q10 is structurally related to menaquinone (vitamin K) and may have procoagulant effects. 

Menaquinone Vitamin K None Carbonyl group and electrons Bacteria, archaea and eukaryotes... 

The shikimate biosynthetic pathway occurs in bacteria, plants, and fungi (including yeasts) and is a major entry into the biosynthesis of primary and secondary metabolites, for example aromatic amino acids, menaquinones, vitamins, and antibiotics [1], Starting from erythrose-4-phosphate (E4P) and phosphoenol-pyruvate... 

Biosynthesis of menaquinone (vitamin K2) and ubiquinone (coenzyme Q) 01MI12. 

Menaquinone (vitamin K2) mediates electron transfer between dehydrogenases and the cytochromes and is the major electron carrier cofactor during anaerobic growth of E. coli. Vitamin K is also an essential cofactor in the post-translational carboxylation of glutamic acid residues in several protein systems [200]. 

Meganathan R (1996) Biosynthesis of the isoprenoid quinones menaquinone (vitamin K2) and ubiquinone (coenzyme Q). In Neidhardt FC, Curtiss III R, Ingraham JL, Lin ECC, Low KB, Magasanik B, Reznikoff WS, Riley M, Schaechter M, Umbarger HE (eds) Escherichia coli and Salmonella typhimurium Cellular and Molecular Biology. Vol 1. ASM, Washington DC, p 642... 

Ubiquinone (UQ), also known as coenzyme Q, has a benzoquinone structure with a long side chain. The name ubiquinone is for the ubiquitous nature of the quinone. Some bacteria also contain menaquinone (vitamin K2), either in addition to ubiquinone or in place of it. For instance, the reaction center of Rhodopseudomonas viridis contains one ubiquinone and one menaquinone, while in some other bacterial reaction centers both quinones are ubiquinones. Menaquinone has a naphthoquinone structure with a long isoprenoid side chain. The long hydrocarbon side chains in ubiquinone and menaquinone render a high degree of hydrophobicity to these molecules. 

MQ - menaquinone (vitamin Kj) MV -methyl viologen MW - molecular weight... 

R. Meganathan 0. Kwon, Biosynthesis ot Menaquinone (Vitamin K2) and Ubiquinone (Coenzyme Q). In EcoSaZ-Escherichia coll and Salmonella Cellular and Molecular Biology A. Bock, R. Curtiss, III, J. B. Kaper, P. D. Karp, F. C. Neidhardt, T. Nystrom,... 

Vitamin K is found in plants as phylloquinone (vitamin Kl) and in animals as menaquinone (vitamin K2). Vitamin K2 is essential for the carboxylation of glutamate residues in certain proteins, to give T-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. 

---