A simple, sensitive spectrophotometric assay system for superoxide dismutase (SOD) has been developed. This assay is based on the inhibitory effects of SOD on the initial rate of 6-hydroxydopamine autoxidation. The inhibition of 6-hydroxydopamine autoxidation was virtually linear to an SOD concentration of approximately 100 ng of SOD/ml (about a 50% inhibition at 100 ng/ml; there was a greater inhibition at higher SOD concentrations). With this assay system it was determined that SOD levels in rat brain, liver, and spinal cord were 84, 660, and 56 μg of SOD/g of tissue, respectively. These results agree very well with results obtained by other assays.
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