Superoxide dismutase (SOD) activity was assayed according to the method of Paoletti and Mocali . This assay is based on the oxidation of nicotinamide adenine dinucleotide reduced disodium salt mediated by a purely chemical reaction sequence which involves EDTA, Mn(II), mercaptoethanol, and molecular oxygen. The decrease of the rate of NADH oxidation is a function of enzyme concentration.