Thermodynamic Characterization of Kidney Superoxide Dismutase from Labeo rohita Exposed to the Mixture of Lead and Chromium

Toxic effect of lead (Pb)+chromium (Cr) mixture on superoxide dismutase (SOD) from kidney of Labeo rohita exposed to sub-lethal concentration for 14 days was evaluated. After purification, specific activity of enzyme was 1750.13 and 1272.72 U mg(-1) in kidney of metal exposed and control fish, respectively. The enzyme from metal exposed kidney was 2.68 fold purified with 58.73 % age recovery. Results of characterization showed that SOD had broad range of pH from 4 to 8.5 but show maximum activity at pH 7 and 7.5 for stressed and control fish, respectively. At 30 degrees C activity of SOD was maximum for both control and stressed fish. At 40 degrees C the enthalpy of denaturation (Delta H*) for metal treated and control fish were 0.373 and 0.736 KJ mol(-1), respectively and decreases with further increase in temperature (70 degrees C) until it was 0.132 and 0.495 KJ mol(-1), respectively. The free energy (Delta G*) of thermal denaturation for metal treated and control fish were 58.45 and 58.79 KJ mol(-1), respectively at 40 degrees C and increases with increase in temperature until it remained 62.65 and 63.18 KJ mol(-1), respectively at 70 degrees C. The negative value of entropy of inactivation (Delta S*) shows that the superoxide dismutase is stable thermodynamically.