Kazuhiro Mitani

Purification and Characterization of Koi Carp (Cyprinus carpio) Acetylcholinesterase


Yoshio KERA@Ryo-hei YAMADA@Shouji TAKAHASHI

Acetylcholinesterase (AChE) hydrolyzes acetylcholine in the synaptic cleft. Since organophosphate and carbamate compounds, important groups of pesticides, strongly inhibit the enzyme, the AChE inhibition in fish tissues is regarded as a good indicator of exposure to the compounds. However, little information is available for enzyme properties of the purified AChE from fishes commonly used for environmental assessment. In the present study, we purified and characterized AChE of Koi carp (Cyprinus carpio) muscle to obtain detailed information of inhibitor specificity.
The solubilization property of the enzyme from the Koi carp muscle indicates that the muscle enzyme is a collagen-tailed asymmetric form. Optimum pH and temperature of the purified enzyme are pH 7.4 - pH 8.0 and 40Ž, respectively. The enzyme is subjected to substrate inhibition at high substrate concentrations. The Vmax/Km values of the enzyme toward acetylthiocholine, propionylthiocholine and butyrylthiocholine are respectively 65.5, 10.1 and 2.17, suggesting that the purified enzyme is in fact AChE. The inhibition potential of the known inhibitors for cholinesterases, organophosphorus pesticides and carbamate pesticides on the Koi carp AChE were determined.