Partial purification and characterization of acetylcholinesterase (AChE) from the estuarine copepod Eurytemora...

Oligohaline copepods such as Eurytemora affinis are widespread in estuaries of northwestern Europe. These minute crustaceans are highly sensitive to contamination and thus serve as useful bioindicators for the monitoring of pollutant effects. The use of decreased cholinesterase (ChE) activity as a sublethal biomarker of exposure to neurotoxic compounds supposes that ChE has been defined in copepods. This study reports the partial purification and characterization of ChE extracted from E. affinis. Analysis by non-denaturing PAGE and by isoelectric focusing indicated that the enzyme is probably a single dimeric form of 140 KDa, with a pI of 6.2. This enzyme is likely an acetylcholinesterase (AChE) since it hydrolyzes acetylthiocholine iodide at a higher rate than other substrates, such as butyrylthiocholine and propionylthiocholine, at pH 7.0 and 25 degrees C, and is inhibited by eserine but not by iso-OMPA. The enzyme exhibited high sensitivity to some of the various pollutants tested. The kinetic properties of this ChE were compared with those of other invertebrate ChEs.