Some Effects of Chlorpromazine on the Activity of Pig Serum Cholinesterase

Abstract

HOFSTEE¹ reported that phenothiazine derivatives inhibited human serum cholinesterase by acting primarily non-competitively with the substrate but competitively with the activating metal since both the metal and drug bind at the anionic site. Preliminary experiments carried out in this laboratory indicated that, using benzoylcholine as substrate, certain phenothiazine derivatives inhibit pig serum cholinesterase in a similar manner. However, when a ‘metal-free’enzyme was prepared by titration with ethylenediamine tetraacetic acid², it was found that concentrations of chlorpromazine below 1 × 10⁻⁶ M activated the enzyme, whereas concentrations above this caused inhibition. Further investigations were, therefore, carried out using different concentrations of metal ions to determine their role in chlorpromazine activation and inhibition of pig serum cholinesterase (Table 1).