A Modification of the Thiocholine Method for the Determination of Cholinesterase. I. Biochemical Evaluation of Selective Inhibitors.

Abstract

Summary. Biochemical controls of the thiocholine method for the determination of cholinesterase have been performed both with partially purified enzyme and with enzymes from the cat. The electrometric method that has been used for the determinations permits the use of the same pH and the presence of all the reagents used histochemically. The inhibition curves of aceto‐and butyrocholinesterase activity using DFP, Mipafox, BW 284c51, 302 IS and 306 IS have been determined. Of these inhibitors BW 284c51 and Mipafox were shown to be the most selective in the histochemical incubation solutions. The compounds were also tested against the crude enzymes from the cat, and showed equally good inhibitory properties. The use of selective substrates and inhibitors is discussed. It is concluded that if biochemical controls of the thiocholine method are to be of value they must be made in exactly the same solution as used histochemically. The pH and the concentration of inhibitor in the solution must be based on controls run in vitro or erroneous localisation of the two types of cholinesterases may result.