An evaluation of the inhibition of human butyrylcholinesterase and acetylcholinesterase by the organophosphate chlorpyrifos oxon
| Autor: | Josephine Shenouda, Paula Green, Lester G. Sultatos |
|---|---|
| Rok vydání: | 2009 |
| Předmět: |
Stereochemistry
Butyrylthiocholine Toxicology Article chemistry.chemical_compound Humans Butyrylcholinesterase Cholinesterase Pharmacology chemistry.chemical_classification Dose-Response Relationship Drug biology Organophosphate Active site Acetylcholinesterase Kinetics Enzyme Acetylthiocholine chemistry Biochemistry Chlorpyrifos biology.protein Cholinesterase Inhibitors |
| Zdroj: | Toxicology and Applied Pharmacology. 241:135-142 |
| ISSN: | 0041-008X |
| DOI: | 10.1016/j.taap.2009.08.014 |
| Popis: | Acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) are enzymes that belong to the superfamily of α/β-hydrolase fold proteins. While they share many characteristics, they also possess many important differences. For example, whereas they have about 54% amino acid sequence identity, the active site gorge of acetylcholinesterase is considerably smaller than that of butyrylcholinesterase. Moreover, both have been shown to display simple and complex kinetic mechanisms, depending on the particular substrate examined, the substrate concentration, and incubation conditions. In the current study, incubation of butyrylthiocholine in a concentration range of 0.005–3.0 mM, with 317 pM human butyrylcholinesterase in vitro, resulted in rates of production of thiocholine that were accurately described by simple Michaelis–Menten kinetics, with a K m of 0.10 mM. Similarly, the inhibition of butyrylcholinesterase in vitro by the organophosphate chlorpyrifos oxon was described by simple Michaelis–Menten kinetics, with a k i of 3048 nM −1 h −1 , and a K D of 2.02 nM. In contrast to inhibition of butyrylcholinesterase, inhibition of human acetylcholinesterase by chlorpyrifos oxon in vitro followed concentration-dependent inhibition kinetics, with the k i increasing as the inhibitor concentration decreased. Chlorpyrifos oxon concentrations of 10 and 0.3 nM gave k i s of 1.2 and 19.3 nM −1 h −1 , respectively. Although the mechanism of concentration-dependent inhibition kinetics is not known, the much smaller, more restrictive active site gorge of acetylcholinesterase almost certainly plays a role. Similarly, the much larger active site gorge of butyrylcholinesterase likely contributes to its much greater reactivity towards chlorpyrifos oxon, compared to acetylcholinesterase. |
| Databáze: | OpenAIRE |
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