Cholinesterases in the domestic fowl and the specificity of some reversible inhibitors

The properties of cholinesterases from several tissues of the domestic fowl have been studied in vitro. Substrate-inhibitor relationships showed that the enzyme corresponding to mammalian acetylcholinesterase resembled the mammalian enzyme in most respects but was considerably less active in its ability to combine with bisquaternary substrates or inhibitors. This suggests some difference between the active sites in the mammalian and the fowl enzymes. The enzyme corresponding to mammalian butyrocholinesterase was found to have properties intermediate between those of mammalian butyrocholinesterase and those of the fowl acetylcholinesterase. “Specific” inhibitors of mammalian butyrocholinesterase were less potent against the corresponding enzyme in the fowl while “specific” inhibitors of mammalian acetylcho-linesterase possessed considerable inhibitory potency against the fowl plasma enzyme. Thus no specific inhibition could be obtained. The enzyme corresponding to butyrocholinesterase, like the fowl acetykholinesterases, was unable to combine with bis-quaternary compounds.