A heat-stable Cu/Zn superoxide dismutase from the viscera of sardinelle (Sardinella aurita): purification and biochemical characterization

Superoxide dismutase (SOD) is an enzyme that protects against oxidative stress from superoxide radicals in living cells. This enzyme was extracted from sardinelle (Sardinella aurita) viscera, purified and characterized. The Cu/Zn-SOD was purified to homogeneity by the three-step procedure consisting of the heating at 65°C for 15 min, precipitation with ammonium sulphate (30–60%, w/v) and Sephadex G-100 gel filtration with a 7.17-fold increase in specific activity. The molecular weight of the native enzyme was estimated to be 40 kDa by G-125 gel filtration on HPLC column and that of the subunit mass, deduced by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, was 20 kDa. Thus the native enzyme appeared to be a homodimer. The optimum pH and temperature for the purified SOD activity were determined to be pH 7.0 and 40°C, respectively. It retained more than 85% of its initial activity after 1 h of incubation at 50°C. The enzyme had a broad stability pH range of 6.0–9.0. The N-terminal sequence of the purified enzyme was VLKAVCVLKGTGEVT. This sequence exhibited a high degree of sequence similarity with other fish Cu/Zn SODs.