Decreased thermal stability of red blood cell glu100-->gly superoxide dismutase from a family with amyotrophic lateral sclerosis.

Familial amyotrophic lateral sclerosis is a degenerative motor neuron disease associated in some cases with the presence of a mutant form of Cu/Zn superoxide dismutase. We have studied the stability of the gly100-->glu mutant in extracts of red cells obtained from members of a family with a history of the disease. Extracts containing the mutant had an average 68% of normal superoxide dismutase activity. On heating at 65 degrees C, these extracts lost activity at twice the rate of extracts containing only the normal enzyme. Decreased heat stability was also evident on native polyacrylamide gel electrophoresis with activity staining. This showed selective loss of first the mutant homodimer and then the heterodimer of the enzyme. Decreased stability intracellularly could be a factor in motor neuron degeneration.