The turnover number of cholinesterase

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Abstract
A mathematical expression was developed for calculating the turnover number of an enzyme, assuming the use of a highly specific irreversible inhibitor to determine the active center concn. The following basic assumptions were involved: (a) the inhibitor is highly specific for the enzyme; (b) inhibition is irreversible; (c) the inhibition reaction is bimolecular. This expression was applied to the study of cholinesterases in tissue extracts, using the inhibitors dicyclohexyl fluorophosphonate and diethyl p-nitrophenylphosphate. The turnover number of erythrocyte cholinesterase determined in this way was found to vary, not only among species, but also among individuals of the same species. It was concluded that the inhibitors were not so highly specific as previously believed. The variations in apparent turnover number were probably due to the presence in the tissue extracts of varying amts. of other substances competing with cholinesterase for the inhibitor.