Thermostable Fe/Mn superoxide dismutase from Bacillus licheniformis SPB-13 from thermal springs of Himalayan region: Purification, characterization and antioxidative potential.

Superoxide dismutase (SOD; EC 1.15.1.1) is an enzyme that scavenges free radicals and increases the longevity. In this study, a thermostable superoxide dismutase (SOD) from Bacillus licheniformis SPB-13, from Himalayan region was purified to homogeneity using ion exchange chromatography (DEAE-Sepharose). The SDS and native PAGE analysis showed that SOD is composed of two subunits of 32 kDa each and total molecular mass of the enzyme was estimated as 68 kDa. The specific activity of enzyme was 3965.51 U/mg and was purified to 16.17 folds. The SOD showed maximum activity with 60 mM Tris-HCl buffer at pH 8.0 for 2 min of incubation. Enzyme along with FeCl3 as metal ion remained active till 70 °C. After reaction variables optimization, enzyme activity increased from 3965.51 to 4015.72 U/mg. Kinetic analysis of SOD showed km of 1.4 mM of NADH and Vmax of 10000 U/mg of protein. Turnover number (kcat) and catalytic efficiency (kcat/Km) were found to be 11,333 s-1 and 7092.2 s-1·mM-1 NADH. The activation energy (Ea) was calculated as 2.67 kJ·mol-1. After typing, it was found to be a member of Fe/Mn SOD family with IC50 value of 25 μg/ml, prevented the cell death at a concentration of 30 μg/ml and it increased the cell viability by 30%.