The "neutral" hydrolysis of simple carboxylic esters in water and the rate enhancements produced by acetylcholinesterase and other carboxylic acid esterases |
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Authors: | Wolfenden Richard Yuan Yang |
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Institution: | Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, 27599-7260, United States. |
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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. |
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