title: The "neutral" hydrolysis of simple carboxylic esters in water and the rate enhancements produced by acetylcholinesterase and other carboxylic acid esterases.
abstract: Experiments at elevated temperatures permit the determination of rate constant and thermodynamic activation parameters for the neutral hydrolysis of the neurotransmitter acetylcholine in water. At 25 °C, the extrapolated rate constant for the uncatalyzed (or neutral) hydrolysis of acetylcholine is 3.9 × 10(-7) s(-1) at 25 °C (ΔH(‡) = 20.0 kcal/mol; TΔS(‡) = -6.1 kcal/mol). Acetylcholine is more susceptible to neutral and base-catalyzed hydrolysis than ethyl acetate but less susceptible to acid-catalyzed hydrolysis. For acetylcholinesterase from the electric eel, the catalytic proficiency [(k(cat)/K(m))/k(neutral)] is 2 × 10(16) M(-1), comparable in magnitude with the catalytic proficiencies of aminohydrolases that act on peptides and nucleosides.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, 27599-7260, United States.
authors.forename: Richard
authors.initials: R
authors.lastname: Wolfenden
authors.forename: Yang
authors.initials: Y
authors.lastname: Yuan
mesh_terms: D019342:Acetic Acid / Q000378:metabolism; D000109:Acetylcholine / Q000378:metabolism; D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D002264:Carboxylic Acids / Q000378:metabolism*; D004593:Electrophorus / Q000378:metabolism; D004950:Esterases / Q000378:metabolism*; D004952:Esters / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D013816:Thermodynamics; D014867:Water / Q000378:metabolism*
chemical_list: D002264:Carboxylic Acids; D004952:Esters; D014867:Water; D004950:Esterases; D000110:Acetylcholinesterase; D000109:Acetylcholine; D019342:Acetic Acid