Model equations for the kinetics of covalent irreversible enzyme inhibition and spontaneous reactivation: Esterases and organophosphorus compounds

Estévez, Jorge; Vilanova, Eugenio

doi:10.1080/10408440802412309

Cited by 45 publications

(51 citation statements)

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“…Two possible interpretations of these observations are (a) the spontaneous hydrolysis of PMSF (James 1978) and/ or (b) the existence of spontaneous reactivation (Estévez and Vilanova 2009).…”

Section: Resultsmentioning

confidence: 97%

“…This indicates that ongoing inhibition during substrate incubation under the assayed conditions is apparently significant, at least for the highest inhibitor concentrations (4 and 10 lM). Therefore, ongoing inhibition during substrate incubation needs to be considered in the model, at least for the most sensitive components (Estévez and Vilanova 2009;Estévez et al 2010). This effect is not highly significant as it is only approximately 10% of the highest inhibitor concentration.…”

Section: Resultsmentioning

confidence: 99%

“…Model equations were applied according to the recommendations provided in previous publications (Estévez and Vilanova 2009).…”

Section: Model Equation For Inhibitionmentioning

confidence: 99%

“…1). Model equations and approaches for analyzing the kinetic behavior of multienzymatic systems in the presence of an inhibitor, either with or without spontaneous reactivation, have been recently reviewed (Estévez and Vilanova 2009). …”

Section: Introductionmentioning

confidence: 99%

“…Usually, the kinetic model assumes that inhibitor concentrations remain constant while the experiment is underway because the inhibitor is tested at least at nano-or micromolar concentrations, while the tested enzyme should be within pico-or femtomolar concentrations. A proposed model equation can only be accepted when different inhibitor concentrations are assayed and if consistent results are obtained as follows: the best-fitting model possesses the same number of components with the same amplitudes and kinetic constants for each tested inhibitor concentrations (Estévez and Vilanova 2009).…”

Section: Introductionmentioning

confidence: 99%

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Kinetics of inhibition of soluble peripheral nerve esterases by PMSF: a non-stable compound that potentiates the organophosphorus-induced delayed neurotoxicity

2012

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The kinetic analysis of esterase inhibition by acylating compounds (organophosphorus carbamates and sulfonyl fluorides) is sometimes unable to yield consistent results by fitting simple inhibition kinetic models to experimental data of complex systems. In this work, kinetic data were obtained for phenylmethylsulfonyl fluoride (PMSF) tested at different concentrations incubated for up to 3 h with soluble fraction of chicken peripheral nerve. PMSF is a protease and esterase inhibitor causing protection or potentiation of the organophosphorus-induced delayed neuropathy and is unstable in water solution. The target of the promotion effect was proposed to be a soluble esterase not yet identified. A kinetic model equation was deduced assuming a multienzymatic system with three different molecular phenomena occurring simultaneously: (1) inhibition, (2) spontaneous chemical hydrolysis of the inhibitor and (3) ongoing inhibition (inhibition during the substrate reaction). A three-dimensional fit of the model was applied for analyzing the experimental data. The best-fitting model is compatible with a resistant component (16.5-18%) and two sensitive enzymatic entities (both 41%). The corresponding second-order rate constants of inhibition (ki = 12.04 × 10⁻² and 0.54 × 10⁻² μM⁻¹ min⁻¹, respectively) and the chemical hydrolysis constant of PMSF (kh = 0.0919 min⁻¹) were simultaneously estimated. These parameters were similar to those deduced in fixed-time inhibition experiments. The consistency of results in both experiments was considered an internal validation of the methodology. The results were also consistent with a significant ongoing inhibition. The proportion of enzymatic components showed in this work is similar to those previously observed in inhibition experiments with mipafox, S9B and paraoxon, demonstrating that this kinetic approach gives consistent results in complex enzymatic systems.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

“…Model equations were applied according to the recommendations provided in previous publications (Estévez and Vilanova 2009).…”

Section: Model Equation For Inhibitionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%