Esterases in the zebra mussel Dreissena polymorpha: Activities, inhibition, and binding to organophosphates

Cholinesterase activities of Dreissena polymorpha were measured colorimetrically. In homogenates of whole control mussel, activities of 125+/-29 mu mol min(-1) kg(-1) were found (n=6). Neither after exposure of Dreissena to organophosphates (thiometon, disulfoton, demeton-S-methyl) nor after addition of demeton-S-methyl (the activated oxygen analogue of thiometon) in vitro was the measured mussel esterase activity inhibited. Esterases of rat, mouse and human tissue showed a 90-100% inhibition. Radiolabelling of the active serine site of esterases in muscle homogenates with H-3-diisopropylfluorophosphate and subsequent separation on polyacrylamide gels revealed similarities as well as differences between rat and mussel esterases. Coomassie-stained muscle proteins of Dreissena showed a different distribution pattern than those of rat. Proteins of rat as well as proteins of mussel with molecular weights between 66 and 97 kDa showed best labelling (highest radioactivity). Proteins with molecular weights greater than 97 kDa were not labelled. Additionally, in Dreissena but not in rat, proteins of around 45 kDa were labelled. The results indicate that the esteratic enzymes in Dreissena were labelled but not inhibited by organophosphates.