V. Talesa et al., Soluble and membrane-bound acetylcholinesterases in Mytilus galloprovincialis (Pelecypoda : Filibranchia) from the northern Adriatic sea, CHEM-BIO IN, 134(2), 2001, pp. 151-166
Three forms of acetylcholinesterase (AChE) were detected in samples of the
bivalve mollusc Mytilus galloprovincialis collected in sites of the Adriati
c sea. Apart from the origin of the mussels, two spontaneously soluble (SS)
AChE occur in the hemolymph and represent about 80% of total activity, per
haps hydrolyzing metabolism-borne choline esters. These hydrophilic enzymes
(forms A and B) copurified by affinity chromatography (procainamide-Sephar
ose gel) and were separated by sucrose gradient centrifugation. They are, r
espectively, a globular tetramer (11.0-12.0 S) and a dimer (6.0-7.0 S) of c
atalytic subunits. The third form, also purified from tissue extracts by th
e same affinity matrix, proved to be an amphiphilic globular dimer (7.0 S)
with a phosphatidylinositol tail giving cell membrane insertion, detergent
(Triton X-100, Brij 96) interaction and self-aggregation. Such an AChE is l
ikely functional in cholinergic synapses. All three AChE forms show a good
substrate specificity and are inactive on butyrylthiocholine. Studies with
inhibitors showed low inhibition by eserine and paraoxon, especially on SS
forms, high sensitivity to 1,5-bis(4-allyldimethylammoniumphenyl)-pentan-3-
one dibromide (BW284c51) and no inhibition with propoxur and diisopropylflu
orophosphate (DFP). The ChE forms in M. galloprovincialis are possibly enco
ded by different genes. Some kinetic features of these enzymes suggest a ge
netic polymorphism. (C) 2001 Elsevier Science Ireland Ltd. All rights reser
ved.