Isozymes of malate-and lactate dehydrogenase of Astyanax bimaculatus as biomarkers of environmental impact

Abstract

The activity of certain isozymes may serve as biomarkers of specific physiological conditions of living organisms. The present work aimed to evaluate malate dehydrogenase (MDH) and lactate dehydrogenase (LDH) isozymes from the hepatic, branchial and renal tissues of the fish Astyanax bimaculatus as biochemical markers of environmental changes in the Una River Basin (Taubaté, SP, Brazil). For this study, the specimens were collected in water bodies located in three sampling sites of the basin, called P1 (Itaim stream), P2 (a stream along the Remédios municipal road) and P3 (a small lake near the Dr. José Luiz Cembranelli municipal road). Physicochemical analysis of the water from these sites indicated that P1 was the less polluted site, P2 presented high levels of electrolytes in water, and P3 presented the worst water quality among the sampling sites. The isoenzymes were separated by native-PAGE and identified by their activity on the polyacrylamide gel. The results indicated that four isozymes of MDH occur in the liver of these fish, and the activities of MDH-1 and MDH-4 were detected only in fish from P2, suggesting that these isoforms have potential as biomarkers of the presence of high levels of electrolytes in water. In the kidney, MDH-1 was detected in fish from P2 and P3, but it was not detected in those from P1, suggesting that the presence of this isozyme may be a biomarker of low-quality water. The gill MDH and LDH isozyme profiles of all tissues examined showed some similarities between individuals from the three collection sites, indicating that they are not suitable as biomarkers of the environmental conditions of these sites.