Amyotrophic lateral sclerosis and structural defects in Cu,Zn superoxide dismutase.

Single-site mutants in the Cu,Zn superoxide dismutase (SOD) gene (SOD1) occur in patients with the fatal neurodegenerative disorder familial amyotrophic lateral sclerosis (FALS). Complete screening of the SOD1 coding region revealed that the mutation Ala4 to Val in exon 1 was the most frequent one; mutations were identified in exons 2, 4, and 5 but not in the active site region formed by exon 3. The 2.4 A crystal structure of human SOD, along with two other SOD structures, established that all 12 observed FALS mutant sites alter conserved interactions critical to the beta-barrel fold and dimer contact, rather than catalysis. Red cells from heterozygotes had less than 50 percent normal SOD activity, consistent with a structurally defective SOD dimer. Thus, defective SOD is linked to motor neuron death and carries implications for understanding and possible treatment of FALS.

Evidence for a digitoxin conjugating UDP-glucuronosyltransferase in the dog.

Liver microsomes of male Beagle dogs contain a form of UDP-glucuronyltransferase which is capable of conjugating digitoxin and its cleavage products digitoxigenin-bisdigitoxoside and digitoxigenin-monodigitoxoside. The highest reaction rates (Vmax 236 pmoles/mg microsomal protein min) were found for digitoxin and digitoxigenin-monodigitoxoside whereas the lowest Km was obtained for digitoxigenin-bisdigitoxoside (29 microM). Digoxin cannot be glucuronidated and digitoxigenin is glucuronidated only in traces. The result may explain the fast digitoxin elimination in dogs. Mutual induction experiments utilizing cardenolides and model substrates of UDP-glucuronyltransferase result in the conclusion that a specific form of UDP-glucuronyltransferase is responsible for glucuronidating digitoxigenin glycosides.