Changes of respiratory chain enzyme activities in growing rat muscle mitochondria.

The activities of three mitochondrial respiratory chain enzymes, namely rotenone sensitive NADH-cytochrome c reductase (NCCR), succinate-cytochrome c reductase (SCCR), and cytochrome c oxidase (CCO) in the extensor digitorum longus muscle were determined in Wistar rats, twenty each, at 3, 4, 5, 6, 10 and 26 weeks of age. The activity of NCCR was extremely low from birth up to 10 weeks of age. The activity of SCCR was stable at 64% to 72% during the first 6 weeks of life and increased to 78% of the adult level at 10 weeks of age. The CCO activity was only 52% of the adult level at 3 weeks of age, increased to 78% to 86% during the next 3 weeks and reached 92% at 10 weeks of age which was not statistically different from the adult level. We conclude that the activities of these 3 respiratory chain enzymes, in muscle mitochondria in rats, were low during development and reached the adult levels at various ages. Before the normal values of these enzyme activities can be established in human pediatric population, age-matched control should be used as the reference value for evaluation of mitochondrial myopathy.