Secondarily reduced cytochrome c oxidase activity in various neuromuscular disorders.

Decreased cytochrome c oxidase (CCO) activity was found in various neuromuscular diseases, including infantile spinal muscular atrophy (SMA) and Fukuyama type congenital muscular dystrophy (FCMD), that was thought to result from a secondarily induced mitochondrial defect. To determine whether or not the enzyme activities in the mitochondrial electron transport system can be secondarily changed, we measured the enzyme activities in denervated rat muscles. The CCO activity decreased progressively to 38-47% of the control value in 3 weeks after denervation, the NADH-cytochrome c reductase and succinate-cytochrome c reductase activities remaining unchanged, suggesting that the CCO activity may be easily reduced secondarily in various disease conditions.