Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.8 (phytase)
 1,997 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mobilization of Ca2+ from microsomal/vacuolar fractions was detected when InsP6-phytase was added after a definite time of hydrolysis which coincides with the time (20-30 min) of optimal production of Ins(2,4,5)P3 bound to phytase. The in vitro constituted Ins(1,4,5)P3 or Ins(2,4,5)P3-phytase complex is also effective in releasing Ca2+. InsP3-phytase complex releases 45% more microsomal Ca2+ than that released by free InsP3 under identical conditions. Other inositol-phytase complexes are ineffective. Furthermore InsP3-phytase complex is recognised by putative receptor associated with microsomal fraction suggesting that the myoinositol tris-phosphate-phytase complex can act as an elicitor in Ca2+ mobilization in plant systems where phytate and phytase occur.
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PMID:Myoinositol tris-phosphate-phytase complex as an elicitor in calcium mobilization in plants. 838 39

In an earlier study a mutant Dictyostelium cell-line (plc-) was constructed in which all phospholipase C activity was disrupted and nonfunctional, yet these cells had nearly normal Ins(1,4,5)P3 levels (Drayer, A.L., Van Der Kaay, J., Mayr, G.W, Van Haastert, P.J.M. (1990) EMBO J. 13, 1601-1609). We have now investigated if these cells have a phospholipase C-independent de novo pathway of Ins(1,4,5)P3 synthesis. We found that homogenates of plc- cells produce Ins(1,4,5)P3 from endogenous precursors. The enzyme activities that performed these reactions were located in the particulate cell fraction, whereas the endogenous substrate was soluble and could be degraded by phytase. We tested various potential inositol polyphosphate precursors and found that the most efficient were Ins(1,3,4,5,6)P5, Ins(1,3,4,5)P4, and Ins(1,4,5,6)P4. The utilization of Ins(1,3,4,5,6)P5, which can be formed independently of phospholipase C by direct phosphorylation of inositol (Stephens, L.R. and Irvine, R.F. (1990) Nature 346, 580-582), provides Dictyostelium with an alternative and novel pathway of de novo Ins(1,4,5)P3 synthesis. We further discovered that Ins(1,3,4,5,6)P5 was converted to Ins(1,4,5)P3 via both Ins(1,3,4,5)P4 and Ins(1,4,5,6)P4. In the absence of calcium no Ins(1,4,5)P3 formation could be observed; half-maximal activity was observed at low micromolar calcium concentrations. These reaction steps could also be performed by a single enzyme purified from rat liver, namely, the multiple inositol polyphosphate phosphatase. These data indicate that organisms as diverse as rat and Dictyostelium possess enzyme activities capable of synthesizing the second messengers Ins(1,4,5)P3 and Ins(1,3,4,5)P4 via a novel phospholipase C-independent pathway.
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PMID:A novel, phospholipase C-independent pathway of inositol 1,4,5-trisphosphate formation in Dictyostelium and rat liver. 853 Mar 62

Although many cells contain large amounts of InsP6, its metabolism and function is still largely unknown. In Dictyostelium lysates, the formation of InsP6 by sequential phosphorylation of inositol via Ins(3,4,6)P3 has been described [Stevens and Irvine (1990) Nature (London) 346, 580-583]; the second messenger Ins(1,4,5)P3 was excluded as a potential substrate or intermediate for InsP6 formation. However, we observed that mutant cells labelled in vivo with [3H]inositol showed altered labelling of both [3H]Ins(1,4,5)P3 and [3H]InsP6. In this report we demonstrate that Ins(1,4,5)P3 is converted into InsP6 in vitro by nucleus-associated enzymes, in addition to the previously described stepwise phosphorylation of inositol to InsP6 that occurs in the cytosol. HPLC analysis indicates that Ins(1,4,5)P3 is converted into InsP6 via sequential phosphorylation at the 3-, 6- and 2-positions. Ins[32P]P6, isolated from cells briefly labelled with [32P]Pi, was analysed using Paramecium phytase, which removes the phosphates of InsP6 in a specific sequence. The 6-position contained significantly more 32P radioactivity than the 4- or 5-positions, indicating that the 6-position is phosphorylated after the other two positions. The results from these in vivo and in vitro experiments demonstrate a metabolic route involving the phosphorylation of Ins(1,4,5)P3 via Ins(1,3,4,5)P4 and Ins(1,3,4,5,6)P5 to InsP6 in a nucleus-associated fraction of Dictyostelium cells.
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PMID:Nucleus-associated phosphorylation of Ins(1,4,5)P3 to InsP6 in Dictyostelium. 855 38

We have undertaken an analysis of the inositol phosphates of Spirodela polyrhiza at a developmental stage when massive accumulation of InsP6 indicates that a large net synthesis is occurring. We have identified Ins3P, Ins(1,4)P2, Ins(3,4)P2 and possibly Ins(4,6)P2, Ins(3,4,6)P3, Ins(3,4,5,6)P4, Ins (1,3,4,5,6)P5, D- and/or L-Ins(1,2,4,5,6)P5 and InsP6 and revealed the likely presence of a second InsP3 with chromatographic properties similar to Ins(1,4,5)P3. The higher inositol phosphates identified show no obvious direct link to pathways of metabolism of second messengers purported to operate in higher plants, nor do they resemble the immediate products of plant phytase action on InsP6.
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PMID:Inositol phosphates in the duckweed Spirodela polyrhiza L. 866 Feb 86

One of the myoinositol trisphosphates produced by the phytase-myoinositol hexakisphosphate (InsP6) reaction is Ins(2,4,5)P3. That Ins(2,4,5)P3 can elicit Ca2+ mobilization from intracellular stores in plants [Samanta, S., Dalal, B., Biswas, S., & Biswas, B.B.(1993) Biochem. Biophys. Res. Commun. 191,427] prompted us to elucidate the mechanism. The InsP3 [Ins(1,4,5)P3/Ins(2,4,5)P3]-phytase complex has been found to interact with the receptor for InsP3 in vitro forming a ternary complex, and a nanomolar concentration of InsP3 is required. For enzymatic cleavage of InsP3 by phytase, micromolar concentrations are needed, and the affinities of the phytase for different myoinositol phosphates have been found to depend upon the number of phosphate groups present in the substrate. Fraction accessibility of tryptophan residues to a neutral fluorescence quencher, acrylamide in free and myoinositol phosphates bound phytase, as determined by Stern-Volmer plot, records a progressive decrease starting from InsP6 to InsP with the notable exceptions of both Ins (1,4,5)P3 and Ins(2,4,5)P3. This deviation from the trend of change in the accessibility of tryptophan residues in myoinositol phosphate bound phytase is recorded from the fact that there is a high affinity (dissociation constant of the nanomolar order) and noncatalytic binding site in phytase for the two isomers of InsP3. In the nanomolar range of concentrations, both isomers of InsP3 bind to a second site of phytase having about 40-fold higher affinity than the normal substrate binding site. InsP3, when bound to noncatalytic site in phytase is not hydrolyzed but induces a significant change in the conformation of phytase as assayed from the relative accessibility of tryptophan residues. This conformational change in phytase is recognized by the receptor for InsP3, because in absence of InsP3 no interaction between the receptor and phytase is detected. However, InsP3-phytase complex is a better elicitor of Ca2+ efflux from microsomal/vacuolar fractions than free InsP3. This is further confirmed by the fact that when Ins(1,3,4)P3-phytase complex can elicit Ca2+ efflux from intracellular stores, Ins(1,3,4)P3 per se is minimally effective.
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PMID:Interaction of myoinositoltrisphosphate-phytase complex with the receptor for intercellular Ca2+ mobilization in plants. 866 92

The characterization of the multiple inositol polyphosphate phosphatase (MIPP) is fundamental to our understanding of how cells control the signalling activities of 'higher' inositol polyphosphates. We now describe our isolation of a 2.3 kb cDNA clone of a rat hepatic form of MIPP. The predicted amino acid sequence of MIPP includes an 18 amino acid region that aligned with approximately 60% identity with the catalytic domain of a fungal inositol hexakisphosphate phosphatase (phytase A); the similarity encompassed conservation of the RHGXRXP signature of the histidine acid phosphatase family. A histidine-tagged, truncated form of MIPP was expressed in Escherichia coli and the enzymic specificity of the recombinant protein was characterized: Ins(1,3,4,5,6)P5 was hydrolysed, first to Ins(1,4,5,6)P4 and then to Ins(1,4,5)P3, by consecutive 3- and 6-phosphatase activities. Inositol hexakisphosphate was catabolized without specificity towards a particular phosphate group, but in contrast, MIPP only removed the beta-phosphate from the 5-diphosphate group of diphosphoinositol pentakisphosphate. These data, which are consistent with the substrate specificities of native (but not homogeneous) MIPP isolated from rat liver, provide the first demonstration that a single enzyme is responsible for this diverse range of specific catalytic activities. A 2.5 kb transcript of MIPP mRNA was present in all rat tissues that were examined, but was most highly expressed in kidney and liver. The predicted C-terminus of MIPP is comprised of the tetrapeptide SDEL, which is considered a signal for retaining soluble proteins in the lumen of the endoplasmic reticulum; the presence of this sequence provides a molecular explanation for our earlier biochemical demonstration that the endoplasmic reticulum contains substantial MIPP activity [Ali, Craxton and Shears (1993) J. Biol. Chem. 268, 6161-6167].
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PMID:Molecular cloning and expression of a rat hepatic multiple inositol polyphosphate phosphatase. 935 36