Nitrogen isotope effects on acetylcholinesterase-catalyzed hydrolysis of o-nitroacetanilide

The nitrogen-15 isotope effect on V/K for Electrophorus electricus acetylcholinesterase-catalyzed hydrolysis of o-nitroacetanilide has been determined by isotope ratio mass spectrometry. The effect determined in buffered H 2 O (0.1 M sodium phosphate, 0.1 N NaCl, pH 7.3, 25 o C) is 15 V/K=1.0119±0.0005. A small though palpable decrease of the isotope effect is observed when the reaction is run in equivalently buffered D 2 O (pD=7.7), 15 V/K=1.0106±0.0002. The corresponding solvent isotope effect is D V/K=1.56±0.03