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)

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

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

Phytic acid is the most abundant inositol phosphate in cells; it constitutes 1-5% of the dry weight of cereal grains and legumes. Phytases are the primary enzymes responsible for the hydrolysis of phytic acid and thus play important roles in inositol phosphate metabolism. A novel alkaline phytase in lily pollen (LlALP) was recently purified in our laboratory. In this paper, we describe the cloning and characterization of LlALP cDNA from lily pollen. Two isoforms of alkaline phytase cDNAs, LlAlp1 and LlAlp2, which are 1467 and 1533 bp long and encode proteins of 487 and 511 amino acids, respectively, were identified. The deduced amino acid sequences contains the signature heptapeptide of histidine phosphatases, -RHGXRXP-, but shares < 25% identity to fungal histidine acid phytases. Phylogenetic analysis reveals that LlALP is most closely related to multiple inositol polyphosphate phosphatase (MINPP) from humans (25%) and rats (23%). mRNA corresponding to LlAlp1 and LlAlp2 were expressed in leaves, stem, petals and pollen grains. The expression profiles of LlAlp isoforms in anthers indicated that mRNA corresponding to both isoforms were present at all stages of flower development. The expression of LlAlp2 cDNA in Escherichia coli revealed the accumulation of the active enzyme in inclusion bodies and confirmed that the cDNA encodes an alkaline phytase. In summary, plant alkaline phytase is a member of the histidine phosphatase family that includes MINPP and exhibits properties distinct from bacterial and fungal phytases.
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PMID:Lily pollen alkaline phytase is a histidine phosphatase similar to mammalian multiple inositol polyphosphate phosphatase (MINPP). 1686 Mar 50