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A critical evaluation of a recent attempt to measure inositol hexakisphosphate (IP6) in mammalian plasma by mass spectroscopy leads to the conclusion that as yet there is no unambiguous evidence that plasma contains any IP6.
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It has been suggested that inositol hexakisphosphate (IP6) contributes to the release of phosphorus (P) from lake sediments, but a mechanistic understanding remains elusive. We investigated the potential mobilization and mineraliz...
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It has been suggested that inositol hexakisphosphate (IP6) contributes to the release of phosphorus (P) from lake sediments, but a mechanistic understanding remains elusive. We investigated the potential mobilization and mineralization of myo- and scyllo-IP6 from the sediment of an oligotrophic Danish lake known to contain high concentrations of inositol phosphates. Solution P-31 NMR spectroscopy was used to determine changes in myo- and scyllo-IP6 in laboratory microcosms incubated under either oxic or anoxic conditions. In addition, we incubated sediment slurries adjusted to pH between 4.9 and 6.6, with and without addition of myo-IP6, and induced redox changes by adding starch and sulfate. We observed no significant changes in myo- or scyllo-IP6 after 1 year of incubation under anaerobic conditions. A sequential extraction procedure revealed that one half of the added myo-IP6 was recovered in the humic acid fraction (acid-insoluble organic matter) and the other half in the fulvic acid fraction (acid-soluble organic matter). Reduction in redox potential by starch addition did not mobilize myo-IP6, but myo-IP6 bound to humic acids was released to the pore water when the pH was increased to ae<yen> 5.8. This pH-induced mobilization of IP6 occurred in parallel with increases in dissolved iron and organic matter, suggesting the release of IP6 bound to humic acids through metal bridges. We conclude that myo-IP6 mobilization from this oligotrophic lake sediment is driven by changes in pH rather than by changes in the redox potential.
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The ability of phytases from fresh fruits and vegetables to degrade phytate in foods was determined in vitro. In contrast to the more consistent presence of phytase in vegetables, only a few fruits contained detectable phytase act...
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The ability of phytases from fresh fruits and vegetables to degrade phytate in foods was determined in vitro. In contrast to the more consistent presence of phytase in vegetables, only a few fruits contained detectable phytase activity. The highest phytase activities were 121 and 97 nmol min~-1 g~-1 in scallion leaves and avocado fruit, respectively.
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Analyses of mutants affecting the synthesis of inositol phosphates have uncovered a variety of new roles for these small molecules in cells, but identification of their physiological targets has lagged behind. New studies on the y...
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Analyses of mutants affecting the synthesis of inositol phosphates have uncovered a variety of new roles for these small molecules in cells, but identification of their physiological targets has lagged behind. New studies on the yeast phosphate starvation response have brought the inositol pyrophosphate IP7 and its mechanism of action into sharp focus.
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The parasitic protozoon Trichomonas vaginalis is the pathogen of trichomoniasis, the most common non-viral, sexually transmitted disease in humans. Inositol phosphates function in the pathomechanisms of a number of human pathogeni...
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The parasitic protozoon Trichomonas vaginalis is the pathogen of trichomoniasis, the most common non-viral, sexually transmitted disease in humans. Inositol phosphates function in the pathomechanisms of a number of human pathogenic protozoa. Recent findings point to a role of inositol phosphates in T. vaginalis' adaption to oxygen exposure during change of host. Six inositol phosphate kinase genes (tvip6k1-4, tvipk1-2) were identified in the T. vaginalis genome by us all coding for proteins containing canonical sequence motifs of the major group of animal inositol phosphate kinases (PDKG, SSLL, DFG/A). When characterizing the purified protein product of tvip6k1, we discovered that the major activity of the highly active enzyme ((similar to)2 mu mol/min/mg) is a conversion of InsP(6) to 6PP-InsP(5) and not 5PP-InsP(5) as by animal isoforms. Thus TvIP6K1 is a novel IP6-6K. The enzyme also converts Ins(1,3,4,5,6)P-5 to products pyrophosphorylated both at 6- and 4-phosphate still having a free 5-hydroxyl. In addition, the enzyme has a minor selectivity to phosphorylate the 3-OH in Ins(1,2,4,5)P-4 and Ins (1,2,4,5,6)P-5 . To present knowledge this novel enzyme is restricted to protozoa. Since its structure is predicted to be distinctly different from animal IP6K (IP6-5K) forms, TvIP6-6K may become a promising target to search for novel trichomoniasis specific drugs.
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Inositol phosphate (IP) kinases constitute an emerging class of cellular kinases linked to multiple cellular activities. Here, we report a previously uncharacterized cellular function in Hedgehog (Hh) signaling for the IP kinase d...
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Inositol phosphate (IP) kinases constitute an emerging class of cellular kinases linked to multiple cellular activities. Here, we report a previously uncharacterized cellular function in Hedgehog (Hh) signaling for the IP kinase designated inositol hexakisphosphate kinase-2 (IP6K2) that produces diphosphoryl inositol phosphates (PP-IPs). In zebrafish embryos, IP6K2 activity was required for normal development of craniofacial structures, somites, and neural crest cells. ip6k2 depletion in both zebrafish and mammalian cells also inhibited Hh target gene expression. Inhibiting IP_6 kinase activity using N(2)-(m-(trifluoromethy)lbenzyl) N(6)-(p-nitrobenzyl) purine (TNP) resulted in altered Hh signal transduction. In zebrafish, restoring IP6K2 levels with exogenous ip6k2 mRNA reversed the effects of IP6K2 depletion. Furthermore, overexpression of ip6k2 in mammalian cells enhanced the Hh pathway response, suggesting IP6K2 is a positive regulator of Hh signaling. Perturbations from IP6K2 depletion or TNP were reversed by overexpressing smoM2, gli1, or ip6k2. Moreover, the inhibitory effect of cyclopamine was reversed by overexpressing ip6k2. This identified roles for the inositol kinase pathway in early vertebrate development and tissue morphogenesis, and in Hh signaling. We propose that IP6K2 activity is required at the level or downstream of Smooth-ened but upstream of the transcription activator Gli1.
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Abstract Diabetes mellitus, as a result of microvascular and macrovascular injury, causes organ dysfunction in a wide variety of tissues. The objective of this study was to investigate the effect of combined inositol hexakisphosph...
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Abstract Diabetes mellitus, as a result of microvascular and macrovascular injury, causes organ dysfunction in a wide variety of tissues. The objective of this study was to investigate the effect of combined inositol hexakisphosphate and inositol supplement on renal and pancreatic integrity in type 2 diabetic rats. Thirty male Sprague-Dawley rats were divided into five groups ( n =6 per group). Type 2 diabetes was induced in three groups using high-fat diet combined with a single dose of streptozotocin (35mg/kg body weight, intraperitoneally). Two of the diabetic groups were treated with combined IP6 and inositol or glibenclamide. Serum biochemical markers of kidney damage kidney, antioxidant status (superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) and lipid peroxidation were measured. Histomorphological and morphometric examinations of the H&E stained pancreas were also carried out. The administration of combined IP6 and inositol supplement resulted in 64% and 27% increase in CAT activities and GSH levels respectively and a 25% decrease in lipid peroxidation level compared to the diabetic control. Serum uric acid, creatinine and BUN levels in the combination treated group was comparable to the normal control. Examination of H&E stained pancreatic sections showed a significant increase (107%) in the number of islets in the combined IP6 and inositol treated group compared to the untreated diabetic group. Overall, the treatment of type 2 diabetic rats with combined IP6 and inositol supplement resulted in the improvement of renal and pancreatic function.
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The inositol phosphates, InsP(5) and InsP(6), have recently been identified as binding partners of fibrinogen, which is critically involved in hemostasis by crosslinking activated platelets at sites of vascular injury. Here, we in...
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The inositol phosphates, InsP(5) and InsP(6), have recently been identified as binding partners of fibrinogen, which is critically involved in hemostasis by crosslinking activated platelets at sites of vascular injury. Here, we investigated the putative physiological role of this interaction and found that platelets increase their InsP(6) concentration upon stimulation with the PLC-activating agonists thrombin, collagen I and ADP and present a fraction of it at the outer plasma membrane.
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The chemical composition of soil phosphorus can vary markedly during pedogenesis, which has implications for phosphorus availability to plant and microbial communities during long-term ecosystem development. We used NaOH-EDTA extr...
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The chemical composition of soil phosphorus can vary markedly during pedogenesis, which has implications for phosphorus availability to plant and microbial communities during long-term ecosystem development. We used NaOH-EDTA extraction and solution P-31 NMR spectroscopy to examine changes in soil phosphorus composition along the Haast chronosequence, a 6,500 year sequence of coastal dunes under lowland temperate rain forest on the west coast of the South Island of New Zealand. Soils along the chronosequence contained a variety of inorganic (orthophosphate, pyrophosphate, and long-chain polyphosphate) and organic (phosphomonoesters, phosphodiesters, and phosphonates) phosphorus compounds, although long-chain polyphosphates were detected only in the organic horizon and phosphonates were detected only in mineral soil. The concentrations of most compounds increased initially during the first few hundred years of pedogenesis and then declined as soils aged. However, concentrations of phospholipids, DNA, and long-chain polyphosphate all increased markedly in the organic horizon of older sites. The four inositol hexakisphosphate stereoisomers (myo, scyllo, neo, and D-chiro) accounted for a considerable proportion of the phosphomonoesters in mineral soil along the sequence (36-52 % of the organic phosphorus), but were not detected in quantifiable concentrations in the youngest mineral soil and all but one organic horizon. Concentrations of the two most abundant isomers (myo- and scyllo) declined along the chronosequence, but the scyllo isomer increased markedly as a proportion of the soil organic phosphorus as soils aged. Amorphous aluminum and iron oxides (i.e., extractable in acid-ammonium oxalate) increased continually throughout the chronosequence, indicating that the decline in inositol hexakisphosphate is due to low phosphorus availability rather than a decline in stabilization potential. Overall, these results provide further evidence that the chemical composition of organic and inorganic phosphorus pools vary markedly during pedogenesis, which has important implications for our understanding of biologically-available organic phosphorus during ecosystem development.
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Inositol 1,3,4,5,6-pentakisphosphate kinase (IP5 2-K) is an enzyme involved in inositol metabolism that synthesizes IP6 (inositol 1,2,3,4,5,6-hexakisphosphate) from inositol 1,3,4,5,6-pentakisphosphate (IP5) and ATP. IP6 is the ma...
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Inositol 1,3,4,5,6-pentakisphosphate kinase (IP5 2-K) is an enzyme involved in inositol metabolism that synthesizes IP6 (inositol 1,2,3,4,5,6-hexakisphosphate) from inositol 1,3,4,5,6-pentakisphosphate (IP5) and ATP. IP6 is the major phosphorus reserve in plants, while in mammals it is involved in multiple cellular events such as DNA editing and chromatin remodelling. In addition, IP6 is the precursor of other highly phosphorylated inositols which also play highly relevant roles. IP5 2-K is the only enzyme that phosphorylates the 2-OH axial position of the inositide and understanding its molecular mechanism of substrate specificity is of great interest in cell biology. IP5 2-K from Arabidopsis thaliana has been expressed in Escherichia coli as two different fusion proteins and purified. Both protein preparations yielded crystals of different quality, always in the presence of IP6. The best crystals obtained for X-ray crystallographic analysis belonged to space group P212121, with unit-cell parameters a = 58.124, b = 113.591, c = 142.478 Å. Several diffraction data sets were collected for the native enzyme and two heavy-atom derivatives using a synchrotron source.
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