| 18423506 |
Sultatos LG, Kaushik R: Altered binding of thioflavin t to the peripheral anionic site of acetylcholinesterase after phosphorylation of the active site by chlorpyrifos oxon or dichlorvos. Toxicol Appl Pharmacol. 2008 Aug 1;230(3):390-6. Epub 2008 Mar 15.
The peripheral anionic site of acetylcholinesterase, when occupied by a ligand, is known to modulate reaction rates at the active site of this important enzyme. The current report utilized the peripheral anionic site specific fluorogenic probe thioflavin t to determine if the organophosphates chlorpyrifos oxon and dichlorvos bind to the peripheral anionic site of human recombinant acetylcholinesterase, since certain organophosphates display concentration-dependent kinetics when inhibiting this enzyme. Incubation of 3 nM acetylcholinesterase active sites with 50 nM or 2000 nM inhibitor altered both the B (max) and K (d) for thioflavin t binding to the peripheral anionic site. However, these changes resulted from phosphorylation of Ser203 since increasing either inhibitor from 50 nM to 2000 nM did not alter further thioflavin t binding kinetics. Moreover, the organophosphate-induced decrease in B (max) did not represent an actual reduction in binding sites, but instead likely resulted from conformational interactions between the acylation and peripheral anionic sites that led to a decrease in the rigidity of bound thioflavin t. A drop in fluorescence quantum yield, leading to an apparent decrease in B (max), would accompany the decreased rigidity of bound thioflavin t molecules. The organophosphate-induced alterations in K (d) represented changes in binding affinity of thioflavin t, with diethylphosphorylation of Ser203 increasing K (d), and dimethylphosphorylation of Ser203 decreasing K (d). These results indicate that chlorpyrifos oxon and dichlorvos do not bind directly to the peripheral anionic site of acetylcholinesterase, but can affect binding to that site through phosphorylation of Ser203. |
164(2,2,2,4) |