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(W/MF143) Enzyme characterisation and season variability of AChE in muscle of Gambusia yucatana from Palizada, Mexico. Rendon-von Osten, Jaime1, Guilhermino, Lúcia2, Arana, Alejandro1, Dzul, Rodolfo1, Soares, Amadeu3, 1 2 3 ABSTRACT- Inhibition of the enzyme acetylcholinesterase in muscle of some fishes has been used as a biomarker of exposure to organophosphate (OP) and carbamate (CB) pesticides. Some studies report differences in fish ChE activity from the same sampling site along the year that was attributed to unidentified pollutants. However, this variation may also be due to the influence of natural variables. For this reason, during a biomonitoring program it is very important to take into consideration the seasonal variability of ChE due to natural factors. The mosquito fish Gambusia yucatana is abundant in rivers and streams of the Yucatan Peninsula; thus ChE activity in muscle of G. yucatana was evaluated in this study as a potential biomarker of OP and CB exposure. The specific objectives of this study were (1) to characterise ChE present in muscle using different substrates and specific inhibitors and (2) to estimate the seasonal variability of ChE activity in fish from different streams. Three streams were sampled during November 1999, January, February, March and July 2000. The rate of substrate hydrolysis of G. yucatana ChE decreased in the order acetylthiocholine, propionylthiocholine and butyrylthiocholine. Excess of substrate inhibited the activity of the enzyme. Eserine sulphate and BW284C51 significantly inhibited the enzyme activity at low concentrations (mM range) and iso-OMPA had no effect up to 8 mM. These findings suggest that the enzyme measured is acetylcholinesterase. No significant differences in ChE activity among fish from different streams were found. The mean of ChE activity was 7.71 nmol/min*mg protein ± 2.30 SD (n= 182) and the variability due to environmental factors was about 30% of this value. Key words: biomarker, cholinesterase, Gambusia yucatana |
