Document Detail

Methyl-paraoxon comparative inhibition kinetics for acetylcholinesterases from brain of neotropical fishes.
MedLine Citation:
PMID:  15451556     Owner:  NLM     Status:  MEDLINE    
Acetylcholinesterase (AChE) sensitivity to the organophosphorus (OP) pesticide methyl-paraoxon was measured in fourteen species of Neotropical marine and freshwater fish found in the waters of Brazil. The rate constant for phosphorylation, kp, the dissociation constant, kd, the second order rate constant, ki, and the IC50 value were measured at 28 degrees C in pH 7.5 buffer for AChE extracted from brain. In addition, the substrate affinity constant, km, was measured with acetylthiocholine. The IC50 for 30 min of inhibition ranged from 123 nM (Prochilodus lineatus) to 3340 nM (Percophis brasiliensis), which corresponded to ki values of 187-6.9 mM(-1) min(-1). A 10-fold range in kp values from 0.21 min(-1) (Paralonchurus brasiliensis) to 2.1 min(-1) (Dules auriga) was associated with a 37-fold range in kd values from 4 to 150 microM. These large differences in reactivity with methyl-paraoxon were not reflected in the binding affinity for acetylthiocholine; km values were approximately 0.1-0.3 mM for all species. These results predict that the amino acid sequence involved in AChE sensitivity differs in these fishes, and that consequently some fish species may be resistant to the toxicity of methyl-paraoxon.
Moacelio V Silva Filho; Manildo M Oliveira; João B Salles; Vera L F Cunha Bastos; Vicente P F Cassano; Jayme Cunha Bastos
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Toxicology letters     Volume:  153     ISSN:  0378-4274     ISO Abbreviation:  Toxicol. Lett.     Publication Date:  2004 Nov 
Date Detail:
Created Date:  2004-09-28     Completed Date:  2004-11-16     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7709027     Medline TA:  Toxicol Lett     Country:  Netherlands    
Other Details:
Languages:  eng     Pagination:  247-54     Citation Subset:  IM    
Faculdade de Farmácia, Universidade Federal Fluminense, 24241-000 Niterói/RJ, Brazil.
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MeSH Terms
Acetylcholinesterase / metabolism*
Brain / enzymology*
Cholinesterase Inhibitors / pharmacology*
Paraoxon / analogs & derivatives*,  pharmacology*
Reg. No./Substance:
0/Cholinesterase Inhibitors; 311-45-5/Paraoxon; 950-35-6/methylparaoxon; EC

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