Bioelectrocatalytical studies of the effect of some pharmaceuticals on the acetylcholinesterase activity

A bioelectrocatalytical method is applied to study the influence of some pharmaceuticals (atropine, caffeine, thiamine, nicotinic acid, quinine and eserine) on the acetylcholinesterase activity. The measuring principle is based on the process of acetylthiocholine hydrolysis, catalyzed by the acetylcholinesterase, immobilized on a graphite electrode surface. The product of this reaction is electroactive and its oxidation current is registered. The kinetics of the process, occurring with the participation of the above mentioned substances, is studied. It is found that competitive (eserine, nicotinic acid, atropine, caffeine) and noncompetitive (thiamine, quinine) inhibition takes place; kinetic parameters of the enzymic reaction (apparent Michaelis constants and constants of inhibition) are determined using electrochemical data, in the absence and in the presence of the inhibitors. It is observed that some of the tested substances behave as activators, under certain conditions. It was found that atropine, caffeine, thiamine, nicotinic acid and quinine do not show any electrochemical activity under the described conditions. Only eserine is oxidized; this however, does not interfere with the enzyme determination in a certain concentration range. Calibration plots, useful for the quantitative analysis, are constructed.