Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.1.8 (cholinesterase)
 12,691 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hydrolysis of substrates by cholinesterases does not follow the Michaelis-Menten reaction mechanism. In addition to the inhibition by excess substrate, these enzymes often show an unexpectedly high activity at low substrate concentrations. It seems that these deviations are the consequence of an unusual architecture of the active site, buried deep inside the core of the molecule. Kinetic data and structural evidence allow for a detailed prediction of the events during a very fast substrate turnover. Recently, we presented a procedure which provides an unbiased framework for mathematical modelling of the complex cholinesterase reaction [J. Stojan, M. Golicnik, D. Fournier, Rational polynomial equation as an unbiased approach for the kinetic studies of Drosophila melanogaster acetylcholinesterase reaction mechanism, Biochim. Biophys. Acta 1703 (2004) 53-61]. It is based on regression analysis of a rational polynomial using classical initial rate data. Here, we extend the use of the rational polynomial rate equation for finding and comparing some selected homeomorphic reaction schemes useful for the mechanistic interpretation of cholinesterase kinetic data.
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PMID:Rational polynomial equation helps to select among homeomorphic kinetic models for cholinesterase reaction mechanism. 1625 94

The inhibition of horse serum butyrylcholinesterase (EC 3.1.1.8) by the organophosphorus compound paraoxon (diethyl 4-nitrophenyl phosphate) was studied by flow microcalorimetry at 37 degrees C in Tris buffer (pH 7.5) using a modification of the kinetic model described by Stojan and coworkers [J. Stojan, V. Marcel, S. Estrada-Mondaca, A. Klaebe, P. Masson, D. Fournier, A putative kinetic model for substrate metabolisation by Drosophila acetylcholinesterase, FEBS Lett. 440 (1998) 85-88]. The reversible steps of the inhibition were studied in the mixing cell of the calorimeter, whereas the irreversible step was studied in the flow-through cell. A new pseudo-first-order approximation was developed to allow the kinetic analysis of inhibition progress curves in the presence of substrate when a significant amount of substrate is transformed. This approximation also allowed one to compute an analytical expression of the calorimetric curves using a gamma distribution to describe the impulse response of the calorimeter. Fitting models to data by nonlinear regression, with simulated annealing as a stochastic optimization method, allowed the determination of all kinetic parameters. It was found that paraoxon binds to both the enzyme and acyl-enzyme, but with weak affinities (K(i) = 0.123 mM and K'(i) = 5.5 mM). A slight activation was observed at the lowest paraoxon concentrations and was attributed to the binding of the substrate to the enzyme-inhibitor complex. The bimolecular inhibition rate constant k(i) = 2.8 x 10(4) M(-1) s(-1) was in agreement with previous studies. It is hoped that the methods developed in this work will contribute to extending the application range of microcalorimetry in the field of irreversible inhibitors.
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PMID:Microcalorimetric study of the inhibition of butyrylcholinesterase by paraoxon. 1934 99