A study on the effect of some pesticides on muscle enzymes of Mediterranean fish

Abstract

The present work incorporates an experimental study of the in vitro effects of the pesticides, aldrin, dimethoate and NRDC 143, on muscle enzymes of three Mediterranean fish species, Boops boops (L.), Coryphaena hippurus (L.) and Mugil cephalus (L.). This work has been prompted by the lack of observations relevant to the effects of pesticide pollution on Mediterranean fish. The pesticides, fish and enzymes studies are considered briefly in Chapter 1 and the aims of the investigation are outlined. A brief review of the literature on the effects of pesticides on aquatic organisms, together with an account of fish muscle metabolism is also included in Chapter 1. Chapter 2 describes experimental methods and computations. Results are given in Chapter 3 together with general observations, and general conclusions are made in Chapter 4. The pesticides included two organochlorine (aldrin and NRDC 143) and an organophosphorus compound (dimethoate). The enzymes were chosen to lied on the pathways of energy-yielding metabolism in anaerobic and aerobic contraction of muscle. They included two enzymes of glycolysis - pyruvate kinase and lactate dehydrogenase; two enzymes of the Krebs tricarboxylic acid cycle - malate dehydrogenase and succinate dehydrogenase and the terminal enzyme of cellular respiration - cytochrome oxidase. Lactate dehydrogenase, malate dehydrogenase, succinate dehydrogenase and cytochrome oxidase were studied in homogenates of red and white muscle after centrifugation of nuclei and cellular debris. Pyruvate kinase was partially purified from white muscle. The kinetic parameters of the enzymes were determined in the presence of 1 ppm and 5 ppm pesticide concentration. The enzymes from the three fish species exhibited similar responses, indicating uniform susceptibility of the fish to the pesticides. While statistically significant trends (at 5 per cent or less probability level) were observed in the maximum velocities, there appeared to be no effect of the pesticides on Michaelis constant (Km) or K0.5 values. Considering the average trend in the pooled data for the three fish, aldrin raised the maximum velocity (Vmax) of pyruvate kinase and lactate dehydrogenase and depressed the maximum velocity of cytochrome oxidase. NRDC 143 raised Vmax of pyruvate kinase and malate dehydrogenase and depressed Vmax of succinate dehydrogenase and cytochrome oxidase. Dimethoate depressed Vmax of succinate dehydrogenase and cytochrome oxidase. The organochlorines, aldrin and NRDC 143, therefore stimulated the extramitochondrial enzymes studies (although malate dehydrogenase is also mitochondrial). While NRDC 143 inhibited both mitochondrial enzymes investigated, aldrin inhibited only cytochrome oxidase. The organophosphorus compound, dimethoate, did not affect the extramitochondrial enzymes but inhibited both mitochondrial enzymes. The inhibitory effect of the pesticides on succinate dehydrogenase and cytochrome oxidase was formally equivalent to non-competitive inhibition since Vmax was depressed without (observable) change in Km.