The invention relates to a novel purified isozyme of an autoclavable superoxide dismutase extracted from the plant Potentilla atrosanguinea Lodd. Var. areyrophylla, said isozyme having the following characteristics, O2− scavenging activity remains same before and after autoclaving; scavenges O2− from sub-zero temperature of −20° C. to high temperature of +80° C.; O2− scavenging activity at 25° C. for 30 days without adding any stabilizing agent such as polyols or sugars; O2− scavenging activity in the presence of saline (0.9% sodium chloride) to 61.8% of the control (without 0.9% sodium chloride), stable at 4° C. for at least 8 months; contamination free and infection free from any living micro- and/or macro-organism after autoclaving; possesses temperature optima at 0° C.; possesses a molecular weight of 33 kD under non-denaturating conditions; possesses a molecular weight of 36 kD under denaturating conditions; has clear peaks in UV range at 268 and 275 nm; has an enzyme turnover number of 19.53×104% per nmol per min at 0° C.; and requires Cu/Zn as a co-factor, method for the preparation of the purified isozyme of autoclavable superoxide dismutase and formulations containing the said autoclavable superoxide dismutase.