Acetylcholinesterase at high catalytic efficiency and substrate specificity in the optic lobe of Eledone moschata (Cephalopoda: Octopoda): biochemical characterization and histochemical localization.
In the optic lobe of the cephalopod mollusc Eledone moschata, two acetylcholinesterase forms I and II were detected, both showing a marked active site specificity with differently sized substrates. Catalytic efficiency (kcat/Km) of the prevailing form II is similar to that of acetylcholinesterases from vertebrate nervous system. Enzyme forms I and II were co-purified from a high-salt-Triton X-100 soluble extract of optic lobe by consecutive affinity chromatographies on procainamide- and concanavalin A-Sepharose columns and then separately obtained by preparative density gradient centrifugation. According to gel-filtration chromatography, sedimentation analysis and SDS-PAGE, the major form II is an amphiphilic globular dimer (135-136 kDa, 6.3-7.4 S) of monomers (66 kDa) S-S linked between terminal segments. Phosphatidylinositol anchors give cell membrane insertion, self-aggregation and detergent (Triton X-100, Brij 97) interaction. Form I, characterized only in part owing to its small amount, showed molecular size (129 kDa) and sedimentation coefficient (7.5 S) similar to those of form II; it is likely to be attached to the cell membrane by electrostatic interactions. Both forms behaved similarly with various inhibitors and underwent excess-substrate inhibition. The results obtained suggest a common origin of both form I and II from a single gene. The former could be a degradation product of the prevailing one (II), which is likely to be functional in cholinergic synapses.
Talesa
V
V
Department of Experimental Medicine, University of Perugia, Italy. biolmgrt@unipg.it
Romani
R
R
Calvitti
M
M
Rosi
G
G
Giovannini
E
E
D000110:Acetylcholinesterase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002384:Catalysis; D002499:Centrifugation, Density Gradient; D004220:Disulfides / Q000737:chemistry; D006651:Histocytochemistry; D007527:Isoenzymes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D015394:Molecular Structure; D008970:Molecular Weight; D008974:Mollusca / Q000201:enzymology*; D009899:Optic Lobe, Nonmammalian / Q000201:enzymology*; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000494:pharmacology
D004220:Disulfides; D007527:Isoenzymes; D000110:Acetylcholinesterase; D010738:Type C Phospholipases