Mitrochondrial NADH dehydrogenase in cystic fibrosis.

We have shown that skin fibroblast from patients with cystic fibrosis (CF) and from carriers for CF [heterozygotes (HZ)] consume more O2 than do their controls. When the mitochondrial electron transport inhibitor rotenone was added to the cells, the relative inhibition of O2 consumption was CF greater than HZ greater than controls (P less than 0.005 in both comparisons). Because rotenone specifically inhibits NADH dehydrogenase, [NADH: (acceptor) oxidoreductase, EC 1.6.99.3], which is the enzyme of energy-conserving site 1 of the mitochondrial electron transport system, activity and kinetics of this enzyme system were studied in fibroblast homogenates. NADH dehydrogenase activity was equal in cells from the three genotypes. At pH 8.0, affinity of the enzyme for its substrate was CF greater than HZ = controls; at pH 8.6, affinity was CF greater than HZ = controls (P less than 0.005 for the differences). pH optima for the genotypes were without exception 8.6 (CF), 8.3 (HZ), and 8.0 (control). HZ and control lines were distinguished unequivocally in a blind test on the basis of differences in pH optima. Purified mitochondrial preparations revealed pH optima identical to those found in whole cell homogenates. These data suggest that the mutant gene responsible for CF is expressed in the complex mitochondrial NADH dehydrogenase system.