Cholinesterases of marine teleost fish: enzymological characterization and potential use in the monitoring of neurotoxic contamination

摘要

Acetylcholinesterase (AChE) is well estabhshed as a biomarker of exposure to organo- phosphate compounds in freshwater fish. By constrast, only a few studies on the enzymology and responsiveness of AChE are available for marine species. In this study, we report char- actenstics of cholinesterases from brain and muscle tissue of three marine teleosts, Limanda limanda, Platichthys fiesus and Serranus cahrilla, to provide basal information for environ- mental monitoring in coastal and marine areas. In brain, cholinesterase activity was exclu- sively comprised of AChE. In contrast, both butyrylcholinesterase (BChE) and AChE were present in axial muscle. The fish BChEs displayed atypical substrate and inhibitor specificities in that they cleaved acetyl-6-(methyl)thiocholine and were sensitive to BW284C51. Bimole- cular inhibition constants, Ki, of BChE for the organophosphates paraoxon and dichlorvos were more than three orders of magnitude greater than the respective Ki values of AChEs. This reflects a much higher sensitivity of BChE to the organophosphates than AChE. Neither AChE from muscle and brain within one species, respectively, nor corresponding cholines- terases from different species differed significantly in their Ki values. The presence of two cholinesterases of differential sensitivity in the same tissue is potentially useful in monitoring.