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Nitrophenyl Acetate (nitrophenyl + acetate)
Selected AbstractsKinetic analysis of effector modulation of butyrylcholinesterase-catalysed hydrolysis of acetanilides and homologous estersFEBS JOURNAL, Issue 10 2008Patrick Masson The effects of tyramine, serotonin and benzalkonium on the esterase and aryl acylamidase activities of wild-type human butyrylcholinesterase and its peripheral anionic site mutant, D70G, were investigated. The kinetic study was carried out under steady-state conditions with neutral and positively charged aryl acylamides [o -nitrophenylacetanilide, o -nitrotrifluorophenylacetanilide and m -(acetamido) N,N,N -trimethylanilinium] and homologous esters (o -nitrophenyl acetate and acetylthiocholine). Tyramine was an activator of hydrolysis for neutral substrates and an inhibitor of hydrolysis for positively charged substrates. The affinity of D70G for tyramine was lower than that of the wild-type enzyme. Tyramine activation of hydrolysis for neutral substrates by D70G was linear. Tyramine was found to be a pure competitive inhibitor of hydrolysis for positively charged substrates with both wild-type butyrylcholinesterase and D70G. Serotonin inhibited both esterase and aryl acylamidase activities for both positively charged and neutral substrates. Inhibition of wild-type butyrylcholinesterase was hyperbolic (i.e. partial) with neutral substrates and linear with positively charged substrates. Inhibition of D70G was linear with all substrates. A comparison of the effects of tyramine and serotonin on D70G versus the wild-type enzyme indicated that: (a) the peripheral anionic site is involved in the nonlinear activation and inhibition of the wild-type enzyme; and (b) in the presence of charged substrates, the ligand does not bind to the peripheral anionic site, so that ligand effects are linear, reflecting their sole interaction with the active site binding locus. Benzalkonium acted as an activator at low concentrations with neutral substrates. High concentrations of benzalkonium caused parabolic inhibition of the activity with neutral substrates for both wild-type butyrylcholinesterase and D70G, suggesting multiple binding sites. Benzalkonium caused linear, noncompetitive inhibition of the positively charged aryl acetanilide m -(acetamido) N,N,N -trimethylanilinium for D70G, and an unusual mixed-type inhibition/activation (, > , > 1) for wild-type butyrylcholinesterase with this substrate. No fundamental difference was observed between the effects of ligands on the butyrylcholinesterase-catalysed hydrolysis of esters and amides. Thus, butyrylcholinesterase uses the same machinery, i.e. the catalytic triad S198/H448/E325, for the hydrolysis of both types of substrate. The differences in response to ligand binding depend on whether the substrates are neutral or positively charged, i.e. the differences depend on the function of the peripheral site in wild-type butyrylcholinesterase, or the absence of its function in the D70G mutant. The complex inhibition/activation effects of effectors, depending on the integrity of the peripheral anionic site, reflect the allosteric ,cross-talk' between the peripheral anionic site and the catalytic centre. [source] The ,-effect in micelles: Nucleophilic substitution reaction of p -nitrophenyl acetate with N -phenylbenzohydroxamate ion,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2006Kallol K. Ghosh Pseudo-first-order rate constants have been determined for the nucleophilic substitution reactions of p -nitrophenyl acetate with p -chlorophenoxide (4-ClC6H4O,) and N -phenylbenzohydroxamate (C6H5CON(C6H5)O,) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij-35) surfactants has been studied. The kobs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and ,-effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26,31, 2006 [source] AN ESTEROLYTIC ACTIVITY FROM A WILD EDIBLE MUSHROOM, LYCOPERDON PERLATUMJOURNAL OF FOOD BIOCHEMISTRY, Issue 4 2009AHMET COLAK ABSTRACT Lycoperdon perlatum Pers. (Lycoperdaceae, Agaricales, Agaricomycetidae, Agaricomycetes, Basidiomycota, Fungi) was evaluated for its esterolytic potential. Native electrophoresis of the crude extracts showed four bands having Rf values of 0.34, 0.39, 0.52 and 0.59. The esterase showed the highest activity toward a short-chain substrate, p -nitrophenyl acetate. Optimum reaction conditions for L. perlatum crude extract were attained at pH 8.0 and 40C. Esterolytic activity of enzyme extract was stimulated in the presence of Mn2+, Fe2+, Ca2+ and Zn2+ in the reaction mixture. The enzyme activity was stimulated by incubation at pH 6.0 but retained 77% of its original activity at its optimum pH after 24 h. Thermal inactivation was displayed after incubation for 20 min at various temperatures above 30C. At 1 mM final concentration, 2-mercaptoethanol, dithiothreitol, ethylenediamine tetraacetic acid and p -methylphenyl sulfonylfluoride inhibited the esterolytic reaction. These results support that the crude L. perlatum extract possesses an esterolytic activity having properties similar to other esterases. PRACTICAL APPLICATIONS Esterases catalyzing the cleavage and formation of ester bonds are known ,/,-hydrolases (EC 3.1.1.X). Esterases are used for the synthesis of flavor esters for the food industry, modification of triglycerides for fat and oil industry and resolution of racemic mixtures used for the synthesis of fine chemicals for the pharmaceutical industry. Therefore, the search for new enzyme sources is important for the development of new enzymes and applications. [source] Functionalized surfactant mediated reactions of carboxylate, phosphate and sulphonate estersJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2010Shuchi Tiwari Abstract Nucleophilic reactivity of some functionalized surfactants, i.e. quaternary pyridinium aldoximes towards the hydrolysis of p -nitrophenyl acetate (PNPA), p -nitrophenyl benzoate (PNPB), p -nitrophenyldiphenyl phosphate (PNPDPP) and p -nitrophenyl p -toluene sulphonate (PNPTS) has been studied at pH 7.1 and 27,°C. Addition of functionalized surfactant to reaction medium causes progressive increase in the rate of hydrolysis and reaches a maximum and then decreases due to further addition of surfactant. An increase in the alkyl chain length of functionalized surfactants resulted in an increase in the first-order rate constant. The apparent pKa and CMC of functionalized surfactants have also been determined by spectrophotometric and conductometric methods, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Immobilization of Candida antarctica lipase B on Polystyrene NanoparticlesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2010Nemanja Mileti Abstract Polystyrene (PS) nanoparticles were prepared via a nanoprecipitation process. The influence of the pH of the buffer solution used during the immobilization process on the loading of Candida antarctica lipase B (Cal-B) and on the hydrolytic activity (hydrolysis of p -nitrophenyl acetate) of the immobilized Cal-B was studied. The pH of the buffer solution has no influence on enzyme loading, while immobilized enzyme activity is very dependent on the pH of adsorption. Cal-B immobilized on PS nanoparticles in buffer solution pH 6.8 performed higher hydrolytic activity than crude enzyme powder and Novozyme 435. [source] Relationship between esterase activity and acrinathrin and methiocarb resistance in field populations of western flower thrips, Frankliniella occidentalis,PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 12 2006Ana C Maymó Abstract The western flower thrips, Frankliniella occidentalis (Pergande), is a serious pest in the south-east of Spain owing to its direct feeding on crops, transmission of the tomato spotted wilt virus and its very high level of resistance to insecticides. Mechanisms of resistance were examined using field populations of F. occidentalis with different susceptibilities to acrinathrin, methiocarb (selective insecticides), endosulfan, metamidophos and deltamethrin (broad-spectrum insecticides). Esterase activity towards ,-naphthyl acetate and p -nitrophenyl acetate in resistant strains was significantly higher than in the reference strain (MLFOM) for both model substrates. This higher activity was significantly correlated with acrinathrin and methiocarb resistance. Copyright © 2006 Society of Chemical Industry [source] Kinetic Measurements of Protein Conformation in a MicrochipBIOTECHNOLOGY PROGRESS, Issue 5 2006Matthew B. Kerby This paper presents a microchip-based system for collecting kinetic time-based information on protein refolding and unfolding. Dynamic protein conformational change pathways were studied in microchannel flow using a microfluidic device. We present a protein-conserving approach for quantifying refolding by dynamically varying the concentration of the chemical denaturants, guanidine hydrochloride and urea. Short diffusion distances in the microchannel result in rapid equilibrium between protein and titrating solutions. Dilutions on the chip were tightly regulated using pressure controls rather than syringe-based flow, as verified with extensive on-chip tracer dye controls. To validate this protein assay method, folding transition experiments were performed using two well-characterized proteins, human serum albumin (HSA) and bovine carbonic anhydrase (BCA). Transition events were monitored through fluorescence intensity shifts of the protein dye 8-anilino-1-naphthalenesulfonic acid (ANS) during dilutions of protein from urea or guanidine hydrochloride solutions. The enzymatic activity of refolded BCA was measured by UV absorption through the conversion of p -nitrophenyl acetate (p-NPA). The microchip protein refolding transitions using ANS were well-correlated with conventional plate-based experiments. The microfluidic platform enables refolding studies to identify rapidly the optimal folding strategy for a protein using small quantities of material. [source] What a Role did Histidine Residue Play in Arylamine N -Acetyltransferase 2 Acetylation?CHINESE JOURNAL OF CHEMISTRY, Issue 10 2006A Quantum Chemistry Study Abstract Arylamine N -acetyltransferases (NATs, EC 2.3.1.5) catalyze an acetyl group transfer from acetyl coenzyme A (AcCoA) to primary arylamines and play a very important role in the metabolism and bioactivation of drugs and carcinogens. Experiments revealed that His-107 was likely the residues responsible for mediating acetyl transfer. The full catalytic mechanism of acetylation process has been examined by density functional theory. The results indicate that, if the acetyl group is directly transferred from the donor, p -nitrophenyl acetate, to the acceptor, cysteine, the high activation energy will be a great hindrance. These energies have dropped in a little range of 20,25 kJ/mol when His-107 assisted the transfer process. However, when protonated His-107 mediated the reaction, the activation energies have been dropped about 73,85 kJ/mol. Our calculations strongly supported an enzyme acetylation mechanism that experiences a thiolate-imidazolium pair, and verified the presumption from experiments. [source] | ||||||||||