PRESENCE OF AN ACETYLCHOLINESTERASE IN THE CNIDARIAN ACTINIA-EQUINA (ANTHOZOA, ACTINIARIA) AND OF A THIOCHOLINE ESTER-HYDROLYZING ESTERASE IN THE SPONGE SPONGIA-OFFICINALIS (DEMOSPONGIAE, KERATOSA)

Cholinesterase (ChE) was studied in Cnidaria (Actinia equina) and in P orifera (Spongia officinalis). In A. equina a single enzyme form was d etected, likely membrane-bound through weak ionic or hydrophobic inter actions. According to gel-filtration chromatography and sedimentation analysis, it seems a G(1) globular monomer (78 kDa, 6.1 S) including s ome hydrophobic domain. This enzyme shows a good active site specifici ty with differently sized substrates. The behaviour with specific ChE inhibitors and substrate inhibition is typical of the acetylcholineste rases and makes it quite distinct from non-specific esterases also pre sent in A. equina. In S. officinalis, ChE-like activity is due to a sm aller hydrophilic protein (50 kDa, 4.8 S). This enzyme shows a very lo w substrate affinity for thiocholine esters, a poor sensitivity for po sitively charged ChE inhibitors and for eserine, as well as absence of substrate inhibition with acetylthiocholine. These results, together with those of electrophoretic analysis, suggest that in S. officinalis a particular esterase form has also fitted for hydrolyzing choline es ters with a low catalytic efficiency. (C) 1996 Wiley-Liss, Inc.