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At least 1,189 records · Page 66Linked to original sources
PubMed2003

Escherichia coli lacking the AcrAB multidrug efflux pump also lacks nonproteinaceous, PHB-polyphosphate Ca2+ channels in the membrane.

PHB(polyP) complexes bind calcium and form calcium channels in the cytoplasmic membrane in Escherichia coli and are likely to be important in Ca(2+) homeostasis in this organism. E. coli N43, which lacks the AcrA component of a major multidrug resistance pump, was shown to be defective in calcium handling, with an inability to maintain submicromolar levels of free Ca(2+) in the cytoplasm. Therefore, using an N-phenyl-1-napthylamine (NPN)-dependent fluorescence assay, we measured temperature-dependent phase transitions in the membranes of intact cells. These transitions specifically depend on the presence of PHB(Ca(2+)polyP) complexes. PHB(Ca(2+)polyP) channel complexes, particularly in stationary phase cultures, were detected in wild-type strains; however, in contrast, isogenic acrA(-) strains had greatly reduced amounts of the complexes. This indicates that the AcrAB transporter may have a novel, hitherto undetected physiological role, either directly in the membrane assembly of the PHB complexes or the transport of a component of the membrane, which is essential for assembly of the complexes into the membrane. In other experiments, we showed that the particular defective calcium handling detected in N43 was not due to the absence of AcrA but to other unknown factors in this strain.

Calcium↗
PubMed2003

The c-Cbl-associated protein and c-Cbl are two new partners of the SH2-containing inositol polyphosphate 5-phosphatase SHIP2.

SHIP2 is a phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) 5-phosphatase which contains motifs susceptible to mediate protein-protein interaction. Using yeast two-hybrid, GST-pulldown, and coimmunoprecipitation studies, we isolated the CAP cDNA as a specific partner of SHIP2 proline-rich domain and showed by GST-pulldown experiments that the interaction took place with the SH3C of CAP. The interaction was not modulated in COS-7 cells stimulated by EGF neither in CHO cells overexpressing the insulin receptor in the presence or absence of insulin stimulation. We also showed that SHIP2 was able to coimmunoprecipitate with endogenous c-Cbl protein in the absence of CAP and with the insulin receptor in CHO-IR cell extracts. The presence of SHIP2 in a complex around the insulin receptor could account for the very specific increase in insulin sensitivity of SHIP2 knock-out mice.

Animals↗
PubMed1991

Accumulation of [3H]-inositol into inositol polyphosphates during development of Dictyostelium.

Inositol hexakisphosphate (InsP6) is present in large amounts during the development of Dictyostelium discoideum although its function is unknown. We have investigated the accumulation of [3H]-labelled inositol into both InsP6 and a more highly charged inositol species called InsPY during development of amoebae on filters. We report that the pattern of [3H]-labelled inositol incorporation into InsP6 and InsPY differs markedly from the pattern seen for inositol phospholipids and inositol(1,4,5)trisphosphate. Incorporation into PtdIns, PtdInsP, PtdInsP2 and Ins(1,4,5)P3 reached plateau values within 4 h. In contrast, incorporation into InsP6 continued in an approximately linear manner for the first eight hours of development. No incorporation into InsPY was seen during the first three hours of development at which time accumulation of [3H] continued linearly in a similar manner as for InsP6. Because the total cell concentration of InsP6 (measured by chemical assay) changes very little during development it seems probable that incorporation of label into InsPY after 3 h is due to a developmentally controlled metabolic switch rather than a requirement for a threshold level of its probable precursor, InsP6.

Animals↗
PubMed1988

Bis-pyridoxal polyphosphates: a new class of specific intramolecular crosslinking agents for hemoglobin.

A series of compounds related to bis-pyridoxal phosphate has been synthesized and used to crosslink deoxyhemoglobin. The yield of crosslinked hemoglobin increased dramatically from about 15% for the di- or triphosphate to about 70% for the tetraphosphate. The site of attachment of the intramolecular crossbridge was found to be from the N-terminal amino group of one beta chain to lysine 82 of the other. Since the distance between these residues is only 11A, the bis-pyridoxal tetraphosphates probably have a "stacked" conformation. The crosslinked hemoglobins bind oxygen cooperatively but with a greatly decreased affinity. The increased ability to unload oxygen together with the stabilization of the tetramer qualifies them as promising cell-free blood substitutes.

Cross-Linking Reagents↗
PubMed2002

Effects of dinucleoside polyphosphates on regulation of coronary vascular tone.

The aim of the present study was to investigate the effects of Xp(5)X and Xp(6)X (X = guanosine (G) or adenosine (A); n = 5 and 6), which have been identified in human platelets, on coronary vascular tone. The activation of purinoceptors in rat coronary vasculature by Xp(5)X and Xp(6)X was evaluated by measuring their effects on perfusion pressure in the Langendorff perfused rat. Ap(5)X and Ap(6)X induced dose-dependent vasodilation that was due to P2Y(1) receptor activation, as evidenced by use of the selective P2Y(1) receptor antagonist 2'-deoxy-N(6)-methyl-adenosine 3',5'-diphosphate diammonium (MRS2179). Vasodilation was induced by NO release, as evidenced by inhibition of nitric oxide synthases (NO synthases) by N(G)-nitro-L-arginine methyl ester (L-NAME). The dose-dependent decrease in coronary perfusion pressure induced by Ap(5)X and Ap(6)X was converted to a dose-dependent increase in perfusion pressure after inhibition of NO synthases by L-NAME. After endothelium removal, the vasodilation elicited by Ap(5)X and Ap(6)X was converted to a vasoconstriction which could be inhibited by P2X receptor blockade. Ap(5)A, Ap(5)G, Ap(6)A and Ap(6)G are vasodilating or vasoconstricting nucleotides that activate P2Y(1) or P2X receptors depending on the status of the coronary vascular endothelium.

Animals↗
PubMed2001

Synthesis of (di)adenosine polyphosphates by non-ribosomal peptide synthetases (NRPS).

In response to nutritional stress conditions, Bacillus brevis produces the cyclodecapeptide antibiotic tyrocidine via tyrocidine synthetase, a multifunctional non-ribosomal peptide synthetase. The apo-form of tyrocidine synthetase 1 forms adenosine (5')tetraphospho(5')adenosine, when incubated with MgATP(2-), amino acid and inorganic pyrophosphatase. The synthesis is an intrinsic property of the adenylation domain, is strictly dependent upon the amino acid, and proceeds from a reverse reaction of adenylate formation involving a second ATP molecule. In the presence of tri- or tetrapolyphosphate preferential synthesis of adenosine 5'-tetraphosphate and adenosine 5'-pentaphosphate occurs, respectively. A potential involvement of adenosine (5')-n-phospho(5')adenosine in the regulation of the biosynthetic process has been suggested.

Adenosine Triphosphate↗
PubMed2000

Localization of mRNA for SHIP2, SH2 domain-containing inositol polyphosphate 5-phosphatase, in the brain of developing and mature rats.

The localization of mRNA for SHIP2, SH2 domain containing inositol 5-phosphatase SHIP isozyme, was examined by in situ hybridization histochemistry in the brain of developing and mature rats. SHIP2 mRNA was first detected in the ventricular germinal zone at embryonic stages. As the postnatal development proceeded, the expression signal was evident in cell of the white matters, presumptive oligodendrocytes, and no significant expression was seen in neurons throughout the development.

Aging↗
PubMedDate not supplied

Accumulation of dinucleoside polyphosphates in Saccharomyces cerevisiae under stress conditions. High levels are associated with cell death.

Adenosine tetraphosphonucleosides (Ap4X) were measured in Saccharomyces cerevisiae by a coupled phosphodiesterase-luciferase assay. After exposure of the cells to cadmium or to hyperthermic treatment (46 degrees C) a marked increase of the cellular pool from 0.08 microM (base level) to 4 microM or higher was observed. The accumulation of Ap4X to high levels is associated with irreversible processes leading to cell death.

Acetates↗