The long-term goal of this application is to understand the mechanism by which over 90 missense mutations in human Cu / Zn superoxide dismutase (SOD1) cause familial amyotrophic lateral sclerosis (FALS), a fatal degenerative disease of the motor neuron system. SOD1 protects the cell against free radical damage by catalyzing the dismutation of superoxide radicals into hydrogen peroxide and molecular oxygen. It was originally believed that a decrease in SOD1 activity was the cause of SOD-related FALS; there is now overwhelming evidence that a gain in an unknown pathological function of mutant SOD1 causes the disease. While the age of disease onset (about47 years) varies little with mutation, disease duration after onset is often mutant-dependent, ranging from 1 to 20 years. The proposed research will test the hypothesis that the pathological function of SOD1 mutants is intimately related to an abnormal SOD1 conformation that is prone to aggregation. The stability, denaturation mechanism, copper and zinc affinity, and the radical-generating ability of the holo, apo, zinc-deficient and copper-deficient states of wild type and selected SOD1 mutants will be investigated. The metal content and the radical-generating activity of aggregated SOD1 will also be studied. Fluorescence, UV / Vis, and circular dichroism spectroscopy will be used to monitor conformational changes in SOD1. The stability, morphology, and association rate of SOD1 aggregates will be studied by various techniques, including polyacrylamide gel electrophoresis, UV / Vis spectroscopy, and electron microscopy. One of the main purposes of the proposed research is to determine the biochemical/biophysical effects of PALS-related SOD1 mutations, and to establish a correlation between these effects and the severity of FALS.