Characteristics of cholinesterase of the earthworm Eisenia foetida

1. Except for pH optimum, reactivation and “aging”, the results indicate that the ChE of Eisenia foetida is distinct from acetylcholinesterase and butyrylcholinesterase. 2. Propionylcholine was found to be a better substrate than acetylcholine, while butyrylcholine, benzoylcholine and acetyl-beta-methylcholine were found to be poor substrates for this ChE. 3. Little or no tendency towards substrate inhibition was seen. 4. The rate constants of inhibition by alkyl phosphates and carbamates favour the concept of this enzyme being a B-esterase, but different from the two main classes of ChE. 5. The buffer-soluble and membrane-bound ChE showed no differences in substrate specificity and Michaelis-Menten constants. 6. These enzymes separately also showed little or no tendency towards substrate inhibition. 7. Crude homogenate, membrane-bound, buffer-soluble and Triton X-100 solubilized ChE, as well as fractions from isoelectric focusing are acted upon by inhibitors at rather similar rates. 8. The presence of only one type of enzyme is therefore indicated. 9. The existence of isoenzymes is not clearly indicated either by isoelectric focusing, by gel electrophoresis technique or density gradient centrifugation. 10. The latter method indicated the molecular weight to be 108,000 ± 7000.