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)

Abstract

Cholinesterase (ChE) was studied in Cnidaria (Actinia equina) and in Porifera (Spongia officinalis). In A. equina a single enzyme form was detected, likely membrane-bound through weak ionic or hydrophobic interactions. According to gel-filtration chromatography and sedimentation analysis, it seems a G1 globular monomer (78 kDa, 6.1 S) including some hydrophobic domain. This enzyme shows a good active site specificity with differently sized substrates. The behaviour with specific ChE inhibitors and substrate inhibition is typical of the acetylcholinesterases and makes it quite distinct from non-specific esterases also present in A. equina. In S. officinalis, ChE-like activity is due to a smaller hydrophilic protein (50 kDa, 4.8 S). This enzyme shows a very low substrate affinity for thiocholine esters, a poor sensitivity for positively 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 esters with a low catalytic efficiency. © 1996 Wiley-Liss, Inc.