Inositol degradation

Anderson, W.A. Magasanik, B. The pathway of myo-inositol degradation in Aerobacter aerogenes. Conversion of 2-deoxy-5-keto-D-gluconic acid to glycolytic intermediates. J. Biol. Chem., 246, 5662-5675 (1971)... 

Phytate (myo-inositol hexaphosphate Fig. 15.3, structure 33) is found in many food species and can be considered as a phytochemical. Its role in the plant is primarily as a phosphate store in seeds, but it is found in other tissues as well, for example, tubers (Harland et al., 2004). Phytate and its hydrolysis products are anti-nutrients that chelate metal ions and thus reduce their bioavailability (Persson et al., 1998 House, 1999). This is particularly a problem with cereal grains, but pre-processing can improve mineral absorption from these foods (Agte and Joshi, 1997). There is some concern that high phytate foods could also contain higher levels of toxic heavy metals caused by natural accumulation. Plants also contain phytate-degrading enzymes that can also influence metal ion bioavailability (Viveros et al., 2000). 

Peptideglycan biosynthesis Metabolism of Complex Lipids Glycerolipid metabolism Inositol phosphate metabolism Sphingophospholipid biosynthesis Phospholipid degradation Sphingoglycolipid metabolism Prostaglandin and leukotriene metabolism... 

Weissman, A. M., and Wojcikiewicz, R. j. H. Inositol 1,4,5-trisphosphate receptor ubiquitmation is mediated by mammalian Ubc7, a component of the endoplasmic reticulum-assodated degradation pathway, and is inhibited by chelation of intracellular Zn +. ]. Biol. Chem. 2003, 278, 38238-46. 

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 intracellular signaltransduction of ofi-adrenoceptors is effectuated by a G-protein-dependent activation of the phospholipase C. This enzyme cleaves phosphatidylinositol, a phospholipid present in cell membranes, into inositol-1,4-5-triphosphate (IP3) and diacylglycerol (DAG). IP3 is a strong inductor of intracellular calcium release which leads to an increase of smooth muscle tone or the liberation of hormones stored in vesicles. Noradrenaline which is released by exocytosis, spreads by diffusion only. Only a small fraction of the total amount of the transmitter released will actually reach the postsynaptic membrane and bind to its specific receptors. Another fraction escapes the synapic cleft by diffusion and is finally enzymatically degraded in the interstitial fluid. Another fraction is taken up postsynaptically and metabolized enzymatically by the target cells (uptake 2). By far most of the transmitter (90%) is actively taken up by the releasing neuron itself (uptake 1 or neuronal re-uptake). In the... 

Ins(l,4,5)P3 is subject to rapid degradation to compounds without any regulatory activity, due to the effects of phosphatases. In addition, there are many other inositol phosphate derivatives (see Berridge Irvine, 1989). Thus, further phosphorylation of Ins(l,4,5)P3 may take place. Of the more highly phosphorylated inositol compounds, Ins(l,4,5,6)P4 in particular is attributed a regulatory function. 

The inositol phosphates are linked into a metabolic cycle (Fig. 6.5) in which they can be degraded and regenerated. Via these pathways, the cell has the ability to replenish stores of inositol phosphate derivatives, according to demand. Ptdins may be regenerated from diacylglycerol via the intermediate levels of phosphatidic acid and CDP-glycerol. 

Lysophospholipids have been found in butter serum by Cho et al. (1977). They characterized the sn-1 and -2 lysophosphatidylcholines and phosphatidylethanolamines. It is not known if these compounds are products of degradation or remnants of biosynthesis. Cho et al. (1977) searched for, but did not find, another possible product of enzymatic degradation of milk, phosphatidic acid. Phosphatidic acid can be formed by the action of phospholipase D on phosphatidylcholine, for example, but this enzymatic activity was not detected. The compound is also an important intermediate in the biosynthesis of lipids, but the concentration in tissue is always very low. The amount is also low in milk. Cho et al. (1977) found 1.2 and 0.9 (percent of total lipid P) of the lyso compounds above. The quantities of the other phospholipids were phosphatidylethanolamine, 27.3 -choline, 29.1 -serine, 13.4 -inositol, 2.5 and sphingomyelin, 25.6. 

Further support for the hypothesis that Ca2+ plays a central role in regulating phytoalexin accumulation is provided by experiments in which the turnover of phosphatidylinositol was measured in the plasma membrane of elicitor-treated carrot cells [17]. The carrot cells were first labelled with [3H]myo-inositol and, after the addition of elicitors, acid extracts of the cells were analyzed chromatographically for the production of inositol trisphosphate (IP3). In cells treated with elicitor, the release of radioactive IP3 increased with time and attained a maximum at 3 - 5 min after treatment. Phospholipase activity responsible for the degradation of phosphorylated phosphatidylinositol increased correspondingly. Several reports have shown that IP3 induces rapid release of Ca2+ from intracellular stores in animal cells [18, 19]. Studies on plant cells have also demonstrated that exogenous IP3 releases Ca2+ from microsomal preparations at micromolar concentrations, although only limited... 

IP3 is rapidly degraded to inactive IP2 and then on to inositol. Meanwhile, diacylglycerol is phosphorylated and then converted to CDP-diacylglycerol, which combines with inositol to form phosphatidylinositol. The latter is subsequently phosphorylated in two steps to PIP2. The degradation and resynthesis of PIP2 completes the so-called phosphatidylinositol cycle. 

In the kiss-and-run mode exocytosis and endocytosis are directly coupled to each other, while in the case of classical complete vesicle fusion, exocytosis and slow clathrin-mediated endocytosis are timely and spatially separated. However, it appears that also in the latter case exocytosis and endocytosis occur coordinated, as both are stimulated by an increase of the cytoplasmic calcium concentration. It has been shown that after calcium entry the enzyme phospho-inositol-5 kinase Iy, which is enriched in the synapse, catalyzes the synthesis of phosphatidylinos-itol (4,5)-bisphosphate and that this mechanism is important for synaptic vesicle trafficking (Di Paolo et al. 2004). As many proteins involved in clathrin-mediated endocytosis are recruited to the plasma membrane by binding to phosphatidylinosi-tol (4,5)-bisphosphate (e.g., amphiphysin, dynamin, epsin, AP-180, and AP-2) it is attractive to speculate that elevated levels of calcium mediate the recruitment of en-docytic proteins to the plasma membrane by this mechanism. The increased level of phosphatidylinositol (4,5)-bisphosphate could be in part degraded by synaptojanin that thereby initiates the disassembly of the clathrin coat. Hence, calcium-induced transient increases in the level of phosphatidylinositol (4,5)-bisphosphate appear to play a central role for coupling exocytosis to clathrin-mediated endocytosis. In addition, it has been demonstrated that calcium also leads to the dephosphorylation of endocytic proteins as amphiphysin, dynamin, and synaptojanin, which in vitro is important for efficient coat assembly (Cousin and Robinson 2001). 

If the dialdose XXXV derived from an inositol reacts in its hemiacetal form XXXVI, it will be degraded to the formate ester of tartronaldehyde... 

The structures of the di-O-isopropylidene acetals of deatfro-inositol and Zero-inositol were determined by lead tetraacetate oxidation, and the results of these degradations confirmed the configurations previously assigned to the two active inositols.1 The dextro compound gave61 the di-O-isopropyl-idene acetal of D-monno-hexodialdose (LVII), which was reduced by sodium... 

Sequoyitol, which is optically inactive, was presumed to be one of the meso forms, and this presumption was eventually verified by the finding that the infrared spectrum of its pentaacetate differs from those of the (optically active) bornesitol pentaacetate and ononitol pentaacetate.66 Many unsuccessful attempts were made to decide between the two possibilities (LXXI and LXXII) by indirect means,78 83 by synthesis,164 and by degradation.68 Proof that sequoyitol is actually 5-O-methyl-myo-inositol (LXXI) was finally obtained by synthesizing it from (+)-pinitol.M The only myoinositol methyl ethers which could be derived from pinitol by the inversion of one of its hydroxyl groups are LXXI and LXXIV formula LXXIV is excluded because it must be optically active. The synthesis of sequoyitol from (+)-l, 2-anhydro-neoinositol (see p. 183) confirms the formula LXXI.7-166... 

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