title: Inactivation of acetylcholinesterase with a bretylium tosylate photoaffinity probe.
abstract: Azidobretylium tosylate (ABT), the p-azido analogue of bretylium tosylate, has been synthesized to serve as a photoaffinity probe for bretylium binding sites. Bretylium tosylate has antiarrhythmic action and also interacts with amiloride-sensitive sodium ion transport sites. Acetylcholinesterase was used as a model protein, and both bretylium and ABT are reversible inhibitors of this enzyme. The kinetic inhibition constants (Ki) were determined to be 40 microM for bretylium tosylate and 6 microM for ABT. The azido compound is photochemically labile and apparently irreversibly inactivates the enzyme. The rate was retarded by the addition of bretylium tosylate or 4-oxo-N,N,N-trimethylpentanaminium iodide (OTI). Sephadex G-25 chromatography further demonstrated the irreversible nature of the photoinactivation. Since ABT binds at or near the acetylcholinesterase active site, it may be a useful probe for the characterization of the enzyme active site.
mesh_terms: D000345:Affinity Labels; D001386:Azides / Q000494:pharmacology*; D001665:Binding Sites; D001949:Bretylium Compounds / Q000378:metabolism* / Q000494:pharmacology*; D001950:Bretylium Tosylate / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology*; D002800:Cholinesterase Inhibitors; D002801:Cholinesterase Reactivators; D002850:Chromatography, Gel; D006868:Hydrolysis; D007700:Kinetics; D010777:Photochemistry; D011220:Pralidoxime Compounds / Q000494:pharmacology
chemical_list: D000345:Affinity Labels; D001386:Azides; D001949:Bretylium Compounds; D002800:Cholinesterase Inhibitors; D002801:Cholinesterase Reactivators; D011220:Pralidoxime Compounds; C050542:4-azidobretylium tosylate; D001950:Bretylium Tosylate; C028797:pralidoxime