ACETYLCHOLINESTERASE IN DENDROBAENA-VENETA (OLIGOCHAETA, OPISHTOPORA)IS PRESENT WITH FORMS SENSITIVE AND INSENSITIVE TO PHOSPHATIDYLINOSITOL PHOSPHOLIPASE-C - BIOCHEMICAL-CHARACTERIZATION AND HISTOCHEMICAL-LOCALIZATION IN THE NERVOUS-SYSTEM

Three distinct acetylcholinesterases were detected in the annelid olig ochaete Dendrobaena veneta. Two enzymes (alpha,beta), copurified from a Triton-X-100-soluble extract of whole animals by affinity (edrophoni um-Sepharose) chromatography, were separately eluted from a Sephadex G -200 column. Gel-filtration chromatography, sedimentation analysis and SDS/PAGE showed the alpha and beta forms to be a globular dimer (110 kDa, 7.0 S) and a hydrophilic monomer (58 kDa, 5.0 S) respectively, bo th weakly linked to the cell membrane. The third form (gamma), also pu rified to homogeneity by slower filtration through an edrophonium-Seph arose matrix, proved to be an amphiphilic globular dimer (133 kDa, 7.0 S) with a phosphatidylinositol anchor giving cell membrane insertion, detergent (Triton X-100, Brij 96) interaction and self-aggregation, T he alpha acetylcholinesterase showed a fairly low substrate specificit y: the beta form hydrolyzed propionylthiocholine at the highest rate a nd was inactive on butyrylthiocholine; the gamma acetylcholinesterase, showing a marked active-site specificity with differently sized subst rates, was likely functional in cholinergic synapses. Studies with inh ibitors showed incomplete inhibition of all three acetylcholinesterase by 1 mM eserine and different sensitivity for edrophonium or procaina mide. The alpha and beta forms, sensitive to .5-bis(4-allyldimethylamm oniumphenyl)-pentan-3-one dibromide, were unaffected by tetra(monoisop ropyl)-pyrophosphortetramide, while both these agents inhibited the ga mma enzyme. All three forms showed excess-substrate inhibition by acet ylthiocholine. Enzyme activity was histochemically localized in the ne rve ring and its minor branches, Monomeric acetylcholinesterase (beta) is likely the only form present in the ganglionic glial framework.