Inositol phosphate abundance

The functional significance of the various edited isoforms of the 5-HT2C receptor has been underscored by their differential abundances of expression in total brain and hypothalamic mRNA populations (293) and distinct functional properties. Moreover, the variant edited receptors exhibit differential abilities to bind various ligands, to mobilize intracellular Ca2+, and to stimulate hydrolysis of inositol phosphates (232,292,293). Bums and colleagues showed that mRNA editing of the 5-HT2C receptor leads to a 10- to 15-fold reduction in the efficacy of the interaction between receptors and their... 

InsPg, also known as phytic acid, was the first inositol phosphate discovered (Posternak, 1919). Initially, InsPg was thought to exist only in plants (mostly legumes) and in the erythrocytes of a few animals. However, it is now known to be ubiquitous in mammalian (and probably all eukaryotic) cells (Heslop et al., 1985), and may actually be the most abundant inositol phosphate. 

Inositol phosphates are often the most abundant organic phosphorus compounds in soils, although they are less common in aquatic samples. They include a sequence of phosphate monoesters, from inositol hexa-kisphosphate to inositol monophosphate (Mandal and Islam, 1979 Harrison, 1987), in various stereoisomeric configurations [myo, scyllo, neo, B-cbiro) of the sugar inositol (Anderson and Malcolm, 1974 Anderson et al., 1974 Cosgrove, 1980 Harrison, 1987 Turner et al, 2002). These compounds are... 

In most soils, phosphate monoesters are the most abundant functional class of organic phosphorus compounds, often constituting >90% of the total organic phosphorus (e.g. Turner et aL, 2003d). They occur mainly as inositol phosphates, predominantly myo-inositol hexakisphos-phate (phytic acid), but also in a range of lower esters and stereoisomers (Harrison, 1987 Turner et aL, 2002b). Phosphate diesters, such as DNA and phospholipids, occur in smaller quantities, of which a sig-... 

Phospholipids containing phosphatidyl, inositol, lecithin, serine, and ethanolamine (Stevenson 1986) are the second most abundant identifiable form of organic P in the upper layer of the subsurface. These groups contain glycerol, fatty acids, and phosphate (Sims and Pierzjinski 2005). The P in the structure is a diester, which is more susceptible to degradation in soils than monoesters. 

The myo-isomer is the most abundant form in nature. It occupies a unique place in inositol metabolism because this is the only isomer synthesized de novo from D-glucose-6-phosphate all other isomers are derived from myo-inositol (Loewus, 1990b Loewus and Murthy, 2000). In early 1900s, myo-inositol was called meso-inositol (abbreviated ms-inositol) probably because, like mesotar-taric acid, it does not exhibit optical activity and cannot be resolved into optical isomers (Posternak, 1965). However, as discussed above, six other isomers also do not exhibit optical activity so the name seemed inappropriate. In 1954, the name myo-inositol was introduced - a name not particularly well coined either since it is a pleonasm - both myo and inositol mean muscle. Nevertheless, the name persists. 

Phosphatidylinositol 4-phosphate (PI-4-P, 3) is the second most abundant inositol phospholipid in biological membranes. It is a product of phosphorylation by four different species of PI 4-kinases (21), and it is a precursor to PI-4,5-P2 and PI-3,4,5-P3. These kinases are the two inositol lipids whose biological roles are understood best. The biological function of PI-4-P is not well known however, the studies in yeast indicate its role extends beyond the substrate for PI 5-kinase (21), such as regulation of vesicular trafficking and protein secretion from Golgi. PI-4-P is removed by the subsequent phosphorylation to PI-4,5-P2 or dephosphorylation to PI by ER-localized phosphatase (21). 

One very promising organophosphorus compound is the abundant, phosphate rich, natural product myo-inositol(hexakisphosphoric acid), or phytic acid. Literature reports on the chemical, environmental, and biological behavior of phytic acid abound 13), Phytic acid is isolated from beans and leafy vegetables and is used as the starting... 

A major fate of PA is conversion to DG that can be metabolized to PC, PE, and TG (Fig. 1). Alternatively, PA can react with CTP to form CDP-DG that is utilized for biosynthesis of the inositol phospholipids as well as phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG) (Fig. 1). Inositol is a cyclohexane derivative in which all six carbons contain hydroxyl groups. The most common inositol isoform is myo-inositol but other less abundant inositols with different structures also occur. The first report of an inositol-containing lipid was in 1930 in Mycobacteria which is ironic since inositol lipids are rarely found in bacteria. Brain is the richest source of inositol-containing lipids, as first discovered by Folch and Wooley in 1942. In 1949, Folch described a PI phosphate (PI-P) that was later found to include PI and PI bisphosphate (PI-P2). The chemical structures of PI, PI-P, and PI-P2 were determined by Ballou and co-workers between 1959 and 1961. PI (1.7 pmol/g liver) constitutes -10% of the phospholipids in cells and tissues. PI-P and PI-P2 are present at much lower concentrations (1-3% of PI). In 1958, Agranoff and co-workers first reported the incorporation of [ HJinositol into PI. Subsequently, Paulus and Kennedy showed that CTP was the preferred nucleotide donor. 

Phytic acid, myo-inositol hexakis (dIhydrogen phosphate), as-l,2,3,S-tnns-4,6-cyclohexanehexol-hexaphosphate a major phosphate storage compound in plants, which is especially abundant in oil seeds, legumes and cereal grains. It is the hexaphosphate of A/yo-inositol (see), in which each OH-group of myoinositol is esterified with phosphoric acid. Calcium and magnesium salts of P.a. are known as phytin. The commercial preparation of myo-inositol involves extraction of P. a. from com (maize) steep liquor, hydrolysis of the P.a. to myo-inositol and inorganic phosphate, and crystallization of the myo-inositol from water. 

Phospholipids are sensitive to autoxidation since they contain an abundance of linoleic acid. The other acid commonly present is palmitic acid. Phospholipids are soluble in chloroform-methanol and poorly soluble in water-free acetone. The pKs value of the phosphate group is between 1 and 2. Phosphatidyl choline and phosphatidyl ethanolamine are zwitter-ions at pH 7. Phospholipids can be hydrolyzed stepwise by alcoholic KOH. Under mild conditions, only the fatty acids are cleaved, whereas, with strong alkalies, the base moiety is released. The bonds between phosphoric acid and glycerol or phosphoric acid and inositol are stable to alkalies, but are readily hydrolyzed by acids. Phosphatidyl derivatives, together with triacylglycerols and sterols, occur in the lipid fraction of lipoproteins (cf. 3.5.1). 

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