KINETIC STUDIES ON THE HYDROLYSIS OF BENZOYLCHOLINE BY HUMAN SERUM CHOLINESTERASE

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Abstract
Benzoylcholine is an unusual substrate for serum cholinesterase because of its high apparent affinity for the enzyme combined with a rapid rate of destruction. The reaction kinetics of the hydrolysis of benzoylcholine can be studied by UV spectrophotometry, since the absorbance decreases in proportion to the concentration of substrate. Kinetic data, obtained by measuring initial reaction rates, or by analyzing continuous hydrolysis curves, are the same within experimental error. The enzymatic data are compatible with the assumption that in the presence of high substrate concentrations a complex is formed consisting of esterase and 2 substrate molecules. This complex is hydrolyzed more slowly than the complex containing one molecule of sub-strate which is formed at low substrate concentrations. Alkaline hydrolysis of benzoylcholine follows the kinetics of a first order reaction.