Effect of sample preparation on analysis of superoxide dismutase activity and isoenzymes

The effect of superoxide dismutase (SOD) activity and isoenzyme pattern of detergents, incubation time, and sonication in the preparation of rat liver samples was investigated. The activity of the manganese form of the enzyme (Mn-SOD) was found to decrease significantly after 4 hr of incubation at room temperature, and activity of the copper, zinc form of the enzyme (Cu, Zn-SOD) was not changed significantly even after 24 hr, although levels were somewhat decreased. Sonication of the sample did not affect Cu, Zn-SOD activity, but total Mn-SOD activity was increased. Addition of detergents did not increase Mn-SOD activity when homogenates were sonicated, indicating that Mn-SOD is not membrane bound. Detergents also had no effect on Cu, Zn-SOD activity. None of the treatments investigated altered the isoenzyme patterns, providing evidence that these isoenzymes are not degradation products.