ESTERASES IN THE ZEBRA MUSSEL DREISSENA-POLYMORPHA - ACTIVITIES, INHIBITION, AND BINDING TO ORGANOPHOSPHATES

Cholinesterase activities of Dreissena polymorpha were measured colori metrically. 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-methy l) nor after addition of demeton-S-methyl (the activated oxygen analog ue of thiometon) in vitro was the measured mussel esterase activity in hibited. Esterases of rat, mouse and human tissue showed a 90-100% inh ibition. Radiolabelling of the active serine site of esterases in musc le homogenates with H-3-diisopropylfluorophosphate and subsequent sepa ration on polyacrylamide gels revealed similarities as well as differe nces between rat and mussel esterases. Coomassie-stained muscle protei ns of Dreissena showed a different distribution pattern than those of rat. Proteins of rat as well as proteins of mussel with molecular weig hts between 66 and 97 kDa showed best labelling (highest radioactivity ). Proteins with molecular weights greater than 97 kDa were not labell ed. Additionally, in Dreissena but not in rat, proteins of around 45 k Da were labelled. The results indicate that the esteratic enzymes in D reissena were labelled but not inhibited by organophosphates.