Monitoring the reaction of carbachol with acetylcholinesterase by thioflavin T fluorescence and acetylthiocholine hydrolysis

Terrone L. Rosenberry, Leilani K. Sonoda, Sarah E. Dekat, Bernadette Cusack, Joseph L. Johnson

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

Acetylcholinesterase (AChE) contains a narrow and deep active site gorge with two sites of ligand binding, an acylation site (or A-site) at the base of the gorge and a peripheral site (or P-site) near the gorge entrance. The P-site contributes to catalytic efficiency by transiently binding substrates on their way to the acylation site, where a short-lived acyl enzyme intermediate is produced. Carbamates are very poor substrates that, like other AChE substrates, form an initial enzyme-substrate complex and proceed to an acylated enzyme intermediate which is then hydrolyzed. However, the hydrolysis of the carbamoylated enzyme is slow enough to resolve the acylation and deacylation steps on the catalytic pathway. Here we show that the reaction of carbachol (carbamoylcholine) with AChE can be monitored both with acetylthiocholine as a reporter substrate and with thioflavin T as a fluorescent reporter group. The fluorescence of thioflavin T is strongly enhanced when it binds to the P-site of AChE, and this fluorescence is partially quenched when a second ligand binds to the A-site to form a ternary complex. These fluorescence changes allow not only the monitoring of the course of the carbamoylation reaction but also the determination of carbachol affinities for the A- and P-sites.

Original languageEnglish (US)
Pages (from-to)235-241
Number of pages7
JournalChemico-biological interactions
Volume175
Issue number1-3
DOIs
StatePublished - Sep 25 2008

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Keywords

  • Acetylcholinesterase
  • Carbamoylation
  • Enzyme mechanism
  • Peripheral site
  • Thioflavin T

ASJC Scopus subject areas

  • Toxicology

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