Catalase Enzyme Response to Chronic Pb+Cd Metal Mixture Exposure, Its Purification and Partial Characterization from the Kidney of Freshwater Fish, Oreochromis niloticus

In the present study, kidney tissues were selected to measure the catalase (CAT) enzyme activity due to their responsibility in the elimination of the compounds generating reactive oxygen species (ROS). Variation in Oreochromis niloticus kidney CAT activity (114.33±0.33 to 159.5±0.03) was observed throughout the study period. During first week of experimental trial, higher CAT activity (159.5±0.03) was noted in Pb+Cd metal mixture stressed fish kidney in comparison to control fish (128.8±0.06). Similarly, lower kidney CAT activity (114.33±0.33) was recorded in second week of experimental trial in metal mixture exposed fish as compared to control group. Significant differences (p<0.05) were observed when compared kidney CAT activity among control and metal mixture stressed O. niloticus. Partial characterization of O. niloticus kidney CAT enzyme after its purification was also performed in this study. Purified kidney CAT showed specific activity 1011.84 and 1314.9 Umg-1 for metal stressed and control fish, respectively. Optimum pH, temperature and substrate concentration both for control and binary metal treated fish purified kidney CAT was measured 7.0, 25°C and 50 mM H2O2, respectively. Km values for control and metal mixture stressed fish were measured 7.59 and 1.17 mM H2O2 mL-1, respectively and Vmax values for control and metal stressed fish were recorded 2.02 and 2.09 UmL-1, respectively. This study will be helpful in understanding how fish oxidative stress biomarker CAT could be used in bio-monitoring studies of metal contamination.