The fundamental kinetics of cholinesterase reaction with substrates and inhibitors in an automated, continuous flow system

Abstract

In the decade between 1950 and 1960 certain cholinesterase inhibiting substances such as many organophosphates and carbamates became important insecticides¹ in hygiene and in plant protection. The toxicological properties of these compounds stimulated the research on cholinesterases in many scientific disciplines; the development of reliable methods for cholinesterase activity determinations has been of particularly great importance. Today one can distinguish between two different categories of practical approaches. The first deals with the experimental determination of the unknown enzyme activity in healthy, unhealthy, and/or poisoned human beings and animals; studies of this kind are important in physiology, toxicology, and clinical chemistry. The second approach, however, is of more interest to the analytical chemist, to whom cholinesterases are nothing but tools for quantitative determinations of unknown amounts of inhibitors; such procedures are frequently applied for residue determinations of certain organophosphates (GAGE 1961). A further important point to be mentioned here is the determination of inhibitor potencies in vitro which are usually expressed in terms of molar inhibitor concentrations causing 50 percent enzyme inhibition (I₅₀-values). Here again the inhibitor concentration is the factor to be determined and the particular type of cholinesterase chosen for the experiment only serves as a necessary reagent for the experiment.