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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two dihydropyridine compounds, Bay K8644 (a calcium entry activator) and nifedipine (a calcium entry blocker), were found to inhibit the binding of [3H]phenylisopropyladenosine ([3H]PIA) to A1 adenosine receptors in rat cerebral cortex membranes with comparable potencies (IC50 10-30 microM). Scatchard analyses indicated that both Bay K8644 and nifedipine inhibited the binding of [3H]PIA by increasing the KD but without significant effect on the Bmax. When tested at 100 microM, neither Bay K8644 nor nifedipine showed a significant effect on [3H]-p-aminoclonidine ([3H]PAC; alpha 2-adrenergic receptor), [3H]dihydroalprenolol ([3H]DHA; beta-adrenergic receptor), [3H]spiperone (dopamine receptor), and [3H]nitrobenzylthioinosine [( 3H]NBMPR; nucleoside transporter) binding. In the presence of 10 mM Mg2+, the ability of 2-chloroadenosine (2-Cl-Ad, an A1 adenosine receptor agonist) to displace [3H]PIA binding was increased. Conversely, the potencies of 1,3-diethyl-8-phenylxanthine (DPX; an A1 receptor antagonist), Bay K8644 and nifedipine in inhibiting [3H]PIA binding were unchanged. It is suggested that both Bay K8644 and nifedipine may act as antagonists of adenosine A1 receptors, in addition to their well-known effects on calcium channels.
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PMID:Inhibition of radioligand binding to A1 adenosine receptors by Bay K8644 and nifedipine. 244 Apr 36

The labelling of rat cerebral cortex alpha 2-adrenoceptors with [3H]-yohimbine ([3H]-YOH) was investigated. At 25 degrees C, binding equilibrium was reached in about 10 min and dissociation occurred with a half time of about 1 min. Saturation experiments gave an equilibrium KD value of 10.13 +/- 1.95 nM and a maximum number of sites of 254 +/- 22 fmol/mg protein. The [3H]-YOH binding sites exhibited alpha 2-adrenergic receptor specificity; the order of potency for the antagonists was rauwolscine greater than yohimbine much greater than prazosin greater than corynanthine. For the agonists, the order was: oxymetazoline greater than clonidine greater than (-)-adrenaline greater than (-)-noradrenaline much greater than (-)-phenylephrine. Agonists exhibited shallow curves in inhibiting [3H]-YOH binding, with pseudo-Hill coefficients (nH) of less than 1.0. These curves were shifted to lower overall affinity and steepened in the presence of 100 microM GTP. Antagonist competition curves were also shallow but GTP had no significant effect. Divalent cations at millimolar concentrations decreased the [3H]-YOH binding: IC50 values were about 6.0, 6.8 and 0.3 mM for Ca2+, Mg2+ and Mn2+ respectively. The maximal number of [3H]-YOH binding sites in the cortex was close to that labelled by the agonist [3H]-paraaminoclonidine ([3H]-PAC). The regional distribution of these sites in the brain, examined at a single concentration of [3H]-YOH and [3H]-PAC, showed a similar pattern except in the striatum. Taken together, the results indicate that like [3H]-PAC, [3H]-YOH labels alpha 2-adrenoceptors in rat brain cortex. They also show that [3H]-YOH is a useful tool for the study of the high and low affinity sites.
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PMID:Characteristics of the [3H]-yohimbine binding on rat brain alpha2-adrenoceptors. 630 Jul

The homotetrameric pyruvate decarboxylase (PDC) from Zymomonas mobilis requires the cofactors thiamin diphosphate and Mg2+ for catalytic activity. We have investigated the role of various amino acid residues in the direct environment of the active site. The role of residue E473 in the catalytic activity and stability of the enzyme was probed by several mutations. All mutant enzymes were either inactive or failed to give any recombinant protein. The close interaction of E473 and N482, which can be deduced from the X-ray structure, has been probed by mutagenesis of N482 to D. This mutation has a significant influence especially on the carboligation reaction of PDC, whereas the binding of the cofactors and the thermostability were not affected. These data suggest a specific interaction of N482 and EA73 which is essential for coordinating the second aldehyde molecule during carboligation. Three hydrophobic residues (L112, I472 and I476) in the vicinity of the active centre have been investigated with respect to their potential influence on the transition states during catalysis. In contrast to L112, I472 and I476 influence the decarboxylation and carboligation reactions. The enlarged substrate-binding site of PDCI472A allows the decarboxylation of longer aliphatic 2-keto acids (C4-C6) as well as aromatic 2-keto acids besides pyruvate. Carboligations using PDCI472A as a catalyst yielded 2-hydroxypropiophenone, benzoin and phenylacetylcarbinol. The enantioselectivity of PAC formation is impaired by mutations of both I472 and I476. The stereochemistry is most significantly affected with the mutant enzyme PDCI476E, which catalyses predominantly the synthesis of (S)-phenylacetylcarbinol.
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PMID:Active site mutants of pyruvate decarboxylase from Zymomonas mobilis--a site-directed mutagenesis study of L112, I472, I476, E473, and N482. 983 41

In this study, the MgCl2/red mud system (MRM) was used to investigate the color removal efficiency of dye solutions. Parameters such as the effect of the dosage of red mud (RM) and MgCl2 have been studied. The effect of pH on the conversion rate of Mg2+ has also been studied. The color removal efficiency of MRM was compared with that of PAC/RM and PAC/NaOH. Meanwhile, the color removal efficiency of RM was compared with that of NaOH. The results show that the MRM system can remove more than 98% of the coloring material at a dosage of 25 g RM/L dye solution and a volume of 1.5 mL MgCl2/L dye solution in the decolorization process of reactive dye, acid dye and direct dye. The color removal efficiency was better than PAC/RM and PAC/NaOH system. The adsorption data have been analyzed using Langmuir and Freundlich isotherms. The results indicated that both models provide the best correlation of the experimental data. The decolorization mechanism of MRM was discussed, too. The MRM system was a viable alternative to some of the more conventional forms of chemical treatment of dye solutions and also provided another way to make use of industrial waste red mud.
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PMID:The color removal of dye wastewater by magnesium chloride/red mud (MRM) from aqueous solution. 1950 55