Maizel_1978_Biokhimiia_43_1150

25 iodomethylates of acetic, propionic, butyric, isobutyric and valeric esters of N-(beta-hydroxyethyl)-derivatives of ephedrine (I) pseudo-ephedrine (II), salsoline (III), salsolidine (IV) and cytisine (V) are studied as substrates and inhibitors of acetylcholine esterase (EC 3.1.1.8) from human erythrocytes and butyrylcholine esterase (EC 3.1.1.8) from horse serum. Butyrylcholine esterase found to increase the hydrolysis rate of all the alkaloid esters studied with the increase of acyl radical either to valerates (for ephedrine and pseudo-ephedrine derivatives), or to butyrates (for the rest alkaloids) and then it did not considerably change under further elongation of carbon chain up to valerate. Isobutyrates were observed to be similar to propionates in their hydrolysis rates. Acetylcholine esterase hydrolyzed acetates with the highest rate, while butyrates of ephedrine and pseudoephedrine derivatives were hydrolyzed by the enzyme 2,5-3-fold as slow as acetates. The rate of choline esterase hydrolysis decreased in the row: ephedrine--salsoline--cytisine with the volumetric increase of the cationic group. The decrease was almost 10-fold for butyrylcholine esterase, while a transition from "poor" substrates to reversible inhibitors was observed for acetylcholine esterase (3 of 5 cytisine esters were reversible inhibitors of the enzyme). The data obtained are compared with literary data on other cyclic choline esterase substrates; they are discussed from the viewpoint of unproductive binding hypothesis and on the basis of the structure of active centres of acetyl- and butyrylcholine esterases.