[24] Quantitation of human cuprozinc superoxide dismutase (SOD-1) by radioimmunoassay and its possible significance in disease

This chapter describes the quantitation of human cuprozinc superoxide dismutase (SOD-l), by radioimmunoassay (RIA), and its possible significance in disease. SODs are enzymes that catalyze the conversion of superoxide free radicals to hydrogen peroxide and oxygen. The amount of SOD-1 in erythrocytes from normal individuals shows very little variation, but increases or decreases in SOD-1 have been noted in several disorders. The reactivity of the anti-SOD-1 antiserum with SOD-1 was shown by the alteration of the electrophoretic mobility of the enzyme after incubation with antiserum. Antiserum or normal rabbit serum was incubated for 16 h at 4° with purified SOD-1, and the mixtures were subjected to polyacrylamide gel electrophoresis, using the tris-glycine buffer system. The RIA for SOD-1 has several advantages over the other methods for quantitation of this enzyme. The RIA provides a direct measurement of the amount of SOD-1 protein and is free of the interference frequently encountered, using enzymatic activity assays. The RIA can be performed on RBC or tissue extracts without precipitating other proteins with chloroform-ethanol. The extraction can give variable recovery of SOD-1 and variable efficiency of precipitation of other proteins.