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Dixon Plots (dixon + plot)
Selected AbstractsMechanism of inhibition of purified leaping mullet (liza saliens) NADPH-cytochrome P450 reductase by toxic metals: Aluminum and thalliumJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 6 2007Azra Bozcaarmutlu Abstract Aluminum and thallium may reach life-threatening levels in aquatic systems in the near future because of their extensive use in various industrial fields. It is therefore important to study the mechanism of toxicity of aluminum and thallium on fish enzymes. To this aim, the effects of aluminum and thallium on the activity of purified leaping mullet (Liza saliens) cytochrome P450 reductase, an essential component of the important cytochrome P450 system, have been studied. Results indicated that both metal ions strongly inhibited the NADPH-cytochrome P450 reductase. The IC50 values of AlCl3 and TlCl3 were estimated to be 34 ,M and 3 ,M, respectively. The Lineweaver,Burk plot and Dixon plot revealed that both metal ions noncompetitively inhibited the purified mullet cytochrome P450 reductase. The Ki values of Al3+ and Tl3+ were calculated from Dixon plots as 8.9 and 5.6 ,M, respectively. The inhibitory effects of Al3+ and Tl3+ on purified cytochrome P450 reductase were partially recovered by 1 mM EDTA. Additionally, tin and magnesium were shown to have no apparent effect on purified mullet cytochrome P450 reductase. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:340,3347, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20200 [source] Molecular characterization, function and regulation of ammonium transporters (Amt) and ammonium-metabolizing enzymes (GS, NADP-GDH) in the ectomycorrhizal fungus Hebeloma cylindrosporumMOLECULAR MICROBIOLOGY, Issue 2 2003Arnaud Javelle Summary External hyphae, which play a key role in nitrogen nutrition of trees, are considered as the absorbing structures of the ectomycorrhizal symbiosis. Here, we have cloned and characterized Hebeloma cylindrosporum AMT1, GLNA and GDHA genes, which encode a third ammonium transporter, a glutamine synthetase and an NADP-dependent glutamate dehydrogenase respectively. Amt1 can fully restore the pseudohyphal growth defect of a Saccharomyces cerevisiae mep2 mutant, and this is the first evidence that a heterologous member of the Mep/Amt family complements this dimorphic change defect. Dixon plots of the inhibition of methylamine uptake by ammonium indicate that Amt1 has a much higher affinity than the two previously characterized members (Amt2 and Amt3) of the Amt/Mep family in H. cylindrosporum. We also identified the intracellular nitrogen pool(s) responsible for the modulation of expression of AMT1, AMT2, AMT3, GDHA and GLNA. In response to exogenously supplied ammonium or glutamine, AMT1, AMT2 and GDHA were downregulated and, therefore, these genes are subjected to nitrogen repression in H. cylindrosporum. Exogenously supplied nitrate failed to induce a downregulation of the five mRNAs after transfer of mycelia from a N-starved condition. Our results demonstrate that glutamine is the main effector for AMT1 and AMT2 repression, whereas GDHA repression is controlled by intracellular ammonium, independently of the intracellular glutamine or glutamate concentration. Ammonium transport activity may be controlled by intracellular NH4+. AMT3 and GLNA are highly expressed but not highly regulated. A model for ammonium assimilation in H. cylindrosporum is presented. [source] Isolation and Enzyme-Inhibition Studies of the Chemical Constituents from Ajuga bracteosaCHEMISTRY & BIODIVERSITY, Issue 1 2007Naheed Riaz Abstract Bractin A (=(2S,3S,4R,5E)-2-{[(2R)-2-hydroxydodecanoyl]amino}triacont-5-ene-1,3,4-triol; 1) and bractin B (=(2S,3S,4R,5E,8E)-2-{[(2R) - 2-hydroxyhexacosanoyl]amino}pentadeca-5,8-diene-3,4,15-triol 1- O - , - D -glucopyranoside; 2), new sphingolipids, and bractic acid (=(5Z,10Z,15Z)-2-decyl-4,7,8,12,13,17,18-heptahydroxy-20,23-dioxopentacosa-5,10,15-trienoic acid; 3), a long-chain polyhydroxy acid, were isolated from the whole plant Ajuga bracteosa along with four known diterpenoids 4,7. Their structures were deduced by spectral studies including 1D- and 2D-NMR spectroscopy. Compounds 1,3 displayed inhibitory potential against enzyme lipoxygenase, while compounds 4,7 inhibited cholinesterase enzymes in a concentration-dependent manner with IC50 values in the range 10.0,33.0, 14.0,35.2, and 10.0,19.0,,M for lipoxygenase, acetylcholinesterase, and butyrylcholinesterase, respectively. Lineweaver,Burk, and Dixon plots, and their secondary replots indicated that all compounds exhibit non-competitive type of inhibition with Ki values in the range of 9.5,35.2, 15.2,36.0, and 11.6,20.5,,M, for lipoxygenase, acetylcholinesterase, and butyrylcholinesterase, respectively. [source] | ||||||||||