PROPERTIES OF CHOLINESTERASE AND CARBOXYLESTERASE OF NERVOUS-TISSUE IN PERIPLANETA-AMERICANA

The rates of enzymic hydrolysis of acetylcholine chloride, acetyl-β-methylcholine chloride, propionylcholine iodide, butyrylcholine iodide, acetylthiocholine iodide (AcTCh) and p-nitrophenyl acetate (p-NPhAc) by homogenates of ganglia from the cockroach Periplaneta americana L. have been studied over a wide range of substrate concentrations. Bimolecular rate constants for the interaction between the esterases hydrolysing these substrates and various organophosphorus inhibitors (OPI) have been determined. The carboxylesterase (CarbE) from cockroach ganglia, which splits p-NPhAc differs from a cholinesterase (ChE) from the same source which hydrolyses choline esters and AcTCh in its sensitivity to some OPI. CarbE as compared with ChE was weakly inhibited by some OPI containing a cationic leaving group and more strongly inhibited by some hydrophobic OPI. Relationships between the structure of the active surface of cockroach ganglion esterases and their sensitivity to OPI are discussed. © 1979.