6-Aminopurines

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M. Kohlhardt - One of the best experts on this subject based on the ideXlab platform.

  • Na+ channel blockade by cyclic AMP and other 6-Aminopurines in neonatal rat heart
    The Journal of Membrane Biology, 1991
    Co-Authors: J. W. Herzig, M. Kohlhardt
    Abstract:

    Elementary Na+ currents were recorded at 19°C in cell attached and inside-out patches from cultured neonatal rat cardiocytes in order to study the effect of cAMP and other 6-Aminopurines.

  • Na^+ channel blockade by cyclic AMP and other 6-Aminopurines in neonatal rat heart
    The Journal of Membrane Biology, 1991
    Co-Authors: J. W. Herzig, M. Kohlhardt
    Abstract:

    Elementary Na^+ currents were recorded at 19°C in cell attached and inside-out patches from cultured neonatal rat cardiocytes in order to study the effect of cAMP and other 6-Aminopurines. The treatment of the cardiocytes with db-cAMP (1×10^−3 mol/liter) led to a decline of reconstructed macroscopic peak I _Na to 62±7.6% of the initial control value. This reduction in NP_0 was mostly accompanied by a decrease in burst activity. Openstate kinetics were preserved even in DPI-modified, noninactivating Na^+ channels. Since the stimulator of the adenylate cyclase, forskolin (1×10^−6 mol/liter), evoked a similar pattern of response, the NP_0 decrease can be considered as the functional correlate of Na^+ channel phosphorylation brought about by cAMP-dependent protein kinase. As found in inside-out patches, cAMP (1×10^−3 mol/liter) remained effective under cell-free conditions and reduced reconstructed macroscopic peak I _NA to about 50% of the initial control value when the absence of Mg-ATP at the cytoplasmic membrane surface prevents phosphorylation reactions. A very similar response developed in the cytoplasmic presence of other 6-Aminopurines including ATP (1×10^3 mol/liter), adenosine (1×10^−4 mol/liter), adenine (1×10^−5 mol/liter) and hypoxanthine (1×10^−5 mol/liter). This susceptibility to adenine suggests that cardiac Na^+ channels in situ could sense intracellular fluctuations of adenine nucleotides, most likely of ATP.

David T F Dryden - One of the best experts on this subject based on the ideXlab platform.

  • 2 aminopurine flipped into the active site of the adenine specific dna methyltransferase m taqi crystal structures and time resolved fluorescence
    Journal of the American Chemical Society, 2007
    Co-Authors: Thomas Lenz, Robert K Neely, David T F Dryden, Eleanor Y M Bonnist, Goran Pljevaljcic, Axel J Scheidig, Anita C Jones, Elmar G. Weinhold
    Abstract:

    We report the crystal structure of the DNA adenine-N6 methyltransferase, M.TaqI, complexed with DNA, showing the fluorescent adenine analog, 2-aminopurine, flipped out of the DNA helix and occupying virtually the same position in the active site as the natural target adenine. Time-resolved fluorescence spectroscopy of the crystalline complex faithfully reports this state:  base flipping is accompanied by the loss of the very short (∼50 ps) lifetime component associated with fully base-stacked 2-aminopurine in DNA, and 2-aminopurine is subject to considerable quenching by π-stacking interactions with Tyr108 in the catalytic motif IV (NPPY). This proves 2-aminopurine to be an excellent probe for studying base flipping by M.TaqI and suggests similar quenching in the active sites of DNA and RNA adenine-N6 as well as DNA cytosine-N4 methyltransferases sharing the conserved motif IV. In solution, the same distinctive fluorescence response confirms complete destacking from DNA and is also observed when the propo...

  • evidence of tautomerism in 2 aminopurine from fluorescence lifetime measurements
    Journal of Physical Chemistry B, 2004
    Co-Authors: Robert K Neely, Steven W Magennis, David T F Dryden, Anita C Jones
    Abstract:

    The fluorescence decay characteristics of 2-aminopurine (2AP) and 2-aminopurine riboside (2APr) have been investigated as a function of excitation and emission wavelength in aqueous and ethanolic solutions. Global analysis of the decay data shows that 2AP exists as two emitting species, whereas 2APr exists as a single species. This is attributed to 9H/7H tautomerism of 2AP. The proportion of 7H tautomer is estimated to be 20% in ethanol and 40% in water.

  • unusual 2 aminopurine fluorescence from a complex of dna and the ecoki methyltransferase
    Nucleic Acids Research, 2004
    Co-Authors: Tsueuju Su, Bernard A Connolly, C Darlington, R Mallin, David T F Dryden
    Abstract:

    The methyltransferase, M.EcoKI, recognizes the DNA sequence 5¢-AACNNNNNNGTGC-3¢ and methylates adenine at the underlined positions. DNA methylation has been shown by crystallography to occur via a base flipping mechanism and is believed to be a general mechanism for all methyltransferases. If no structure is available, the fluorescence of 2-aminopurine is often used as a signal for base flipping as it shows enhanced fluorescence when its environment is perturbed. We find that 2-aminopurine gives enhanced fluorescence emission not only when it is placed at the M.EcoKI methylation sites but also at a location adjacent to the target adenine. Thus it appears that 2-aminopurine fluorescence intensity is not a clear indicator of base flipping but is a more general measure of DNA distortion. Upon addition of the cofactor S-adenosylmethionine to the M.EcoKI:DNA complex, the 2aminopurine fluorescence changes to that of a new species showing excitation at 345 nm and emission at 450 nm. This change requires a fully active enzyme, the correct cofactor and the 2-aminopurine located at the methylation site. However, the new fluorescent species is not a covalently modified form of 2-aminopurine and we suggest that it represents a hitherto undetected physicochemical form of 2-aminopurine.

Elmar G. Weinhold - One of the best experts on this subject based on the ideXlab platform.

  • 2 aminopurine flipped into the active site of the adenine specific dna methyltransferase m taqi crystal structures and time resolved fluorescence
    Journal of the American Chemical Society, 2007
    Co-Authors: Thomas Lenz, Robert K Neely, David T F Dryden, Eleanor Y M Bonnist, Goran Pljevaljcic, Axel J Scheidig, Anita C Jones, Elmar G. Weinhold
    Abstract:

    We report the crystal structure of the DNA adenine-N6 methyltransferase, M.TaqI, complexed with DNA, showing the fluorescent adenine analog, 2-aminopurine, flipped out of the DNA helix and occupying virtually the same position in the active site as the natural target adenine. Time-resolved fluorescence spectroscopy of the crystalline complex faithfully reports this state:  base flipping is accompanied by the loss of the very short (∼50 ps) lifetime component associated with fully base-stacked 2-aminopurine in DNA, and 2-aminopurine is subject to considerable quenching by π-stacking interactions with Tyr108 in the catalytic motif IV (NPPY). This proves 2-aminopurine to be an excellent probe for studying base flipping by M.TaqI and suggests similar quenching in the active sites of DNA and RNA adenine-N6 as well as DNA cytosine-N4 methyltransferases sharing the conserved motif IV. In solution, the same distinctive fluorescence response confirms complete destacking from DNA and is also observed when the propo...

  • 2 aminopurine as a fluorescent probe for dna base flipping by methyltransferases
    Nucleic Acids Research, 1998
    Co-Authors: Birgit Holz, Saulius Klimasauskas, Saulius Serva, Elmar G. Weinhold
    Abstract:

    DNA base flipping, which was first observed for the C5-cytosine DNA methyltransferase M. Hha I, results in a complete removal of the stacking interactions between the target base and its neighbouring bases. We have investigated whether duplex oligodeoxynucleotides containing the fluorescent base analogue 2-aminopurine can be used to sense DNA base flipping. Using M. Hha I as a paradigm for a base flipping enzyme, we find that the fluorescence intensity of duplex oligodeoxynucleotides containing 2-aminopurine at the target site is dramatically enhanced (54-fold) in the presence of M. Hha I. Duplex oligodeoxynucleotides containing 2-aminopurine adjacent to the target cytosine show little fluorescence increase upon addition of M. Hha I. These results clearly demonstrate that duplex oligodeoxynucleotides containing 2-aminopurine at the target site can serve as fluorescence probes for base flipping. Another enzyme hypothesized to use a base flipping mechanism is the N6-adenine DNA methyltransferase M. Taq I. Addition of M. Taq I to duplex oligodeoxynucleotides bearing 2-aminopurine at the target position, also results in a strongly enhanced fluorescence (13-fold), whereas addition to duplex oligodeoxynucleotides containing 2-aminopurine at the 3'- or 5'-neighbouring position leads only to small fluorescence increases. These results give the first experimental evidence that the adenine-specific DNA methyltransferase M. Taq I also flips its target base.

Shuitein Chen - One of the best experts on this subject based on the ideXlab platform.

  • the screening and characterization of 6 aminopurine based xanthine oxidase inhibitors
    Bioorganic & Medicinal Chemistry, 2007
    Co-Authors: Jungfeng Hsieh, Shihhsiung Wu, Keefong Choong, Shuitein Chen, Yuliang Yang
    Abstract:

    : Xanthine oxidase (XO) is a key enzyme which can catalyze xanthine to uric acid causing hyperuricemia in humans. By using the fractionation technique and inhibitory activity assay, an active compound that prevents XO from reacting with xanthine was isolated from wheat leaf. It was identified by the Mass and NMR as 6-aminopurine (adenine). A structure-activity study based on 6-aminopurine was conducted. The inhibition of XO activity by 6-aminopurine (IC(50)=10.89+/-0.13 microM) and its analogues was compared with that by allopurinol (IC(50)=7.82+/-0.12 microM). Among these analogues, 2-chloro-6(methylamino)purine (IC(50)=10.19+/-0.10 microM) and 4-aminopyrazolo[3,4-d] pyrimidine (IC(50)=30.26+/-0.23 microM) were found to be potent inhibitors of XO. Kinetics study showed that 2-chloro-6(methylamino)purine is non-competitive, while 4-aminopyrazolo[3,4-d]pyrimidine is competitive against XO.

J. W. Herzig - One of the best experts on this subject based on the ideXlab platform.

  • Na+ channel blockade by cyclic AMP and other 6-Aminopurines in neonatal rat heart
    The Journal of Membrane Biology, 1991
    Co-Authors: J. W. Herzig, M. Kohlhardt
    Abstract:

    Elementary Na+ currents were recorded at 19°C in cell attached and inside-out patches from cultured neonatal rat cardiocytes in order to study the effect of cAMP and other 6-Aminopurines.

  • Na^+ channel blockade by cyclic AMP and other 6-Aminopurines in neonatal rat heart
    The Journal of Membrane Biology, 1991
    Co-Authors: J. W. Herzig, M. Kohlhardt
    Abstract:

    Elementary Na^+ currents were recorded at 19°C in cell attached and inside-out patches from cultured neonatal rat cardiocytes in order to study the effect of cAMP and other 6-Aminopurines. The treatment of the cardiocytes with db-cAMP (1×10^−3 mol/liter) led to a decline of reconstructed macroscopic peak I _Na to 62±7.6% of the initial control value. This reduction in NP_0 was mostly accompanied by a decrease in burst activity. Openstate kinetics were preserved even in DPI-modified, noninactivating Na^+ channels. Since the stimulator of the adenylate cyclase, forskolin (1×10^−6 mol/liter), evoked a similar pattern of response, the NP_0 decrease can be considered as the functional correlate of Na^+ channel phosphorylation brought about by cAMP-dependent protein kinase. As found in inside-out patches, cAMP (1×10^−3 mol/liter) remained effective under cell-free conditions and reduced reconstructed macroscopic peak I _NA to about 50% of the initial control value when the absence of Mg-ATP at the cytoplasmic membrane surface prevents phosphorylation reactions. A very similar response developed in the cytoplasmic presence of other 6-Aminopurines including ATP (1×10^3 mol/liter), adenosine (1×10^−4 mol/liter), adenine (1×10^−5 mol/liter) and hypoxanthine (1×10^−5 mol/liter). This susceptibility to adenine suggests that cardiac Na^+ channels in situ could sense intracellular fluctuations of adenine nucleotides, most likely of ATP.