FUNCTION: Destroys radicals which are normally produced within the cells and which are toxic to biological systems. CATALYTIC ACTIVITY: 2 superoxide + 2 H+ = O2 + H2O2. COFACTOR: Binds 1 copper ion per subunit. COFACTOR: Binds 1 zinc ion per subunit. SUBUNIT: Homodimer. SUBCELLULAR LOCATION: Cytoplasm. DISEASE: Defects in SOD1 are the cause of familial amyotrophic lateral sclerosis (FALS); also called amyotrophic lateral sclerosis 1 (ALS1 or ALS). ALS is a degenerative disorder of motorneurons in the cortex, brainstem and spinal cord. ALS is characterized by muscular weakness and atrophy beginning in the hands and spreading to the forearms and legs. Muscle fasciculations are commonly visible. Sensory abnormalities are absent. Death usually occurs within 2 to 5 years. ALS is sometimes referred to as Lou Gehrig disease after the famous American baseball player who was diagnosed with the disorder. FALS, the familial form of ALS, accounts for about 10% of the cases and is transmitted in an autosomal dominant manner. The mean age at onset of FALS is 45 years. MISCELLANEOUS: Zinc binding promotes dimerization. SIMILARITY: Belongs to the Cu-Zn superoxide dismutase family.