A gene from Withania somnifera (winter cherry), encoding a highly stable chloroplastic Cu/Zn superoxide dismutase (SOD), was cloned and expressed in Escherichia coli. The recombinant enzyme (specific activity of similar to 4,200 U mg(-1)) was purified and characterized. It retained similar to 90 and similar to 70% residual activities after 1 h at 80 and 95 degrees C, respectively. At 95 degrees C, thermal inactivation rate constant (K(d)) of the enzyme was 2.46 9 10(-3) min(-1) and half-life of heat inactivation was 4.68 h. The enzyme was stable against a broad pH range (2.5-11.0). It also showed a high degree of resistance to detergent, ethanol and protease digestion. This recombinant Cu/Zn SOD could therefore have useful applications.