Ageing is associated in females with a decline in the content and activity on the b-c1 complex in skeletal muscle mitochondria.

The activity of cytochrome-c oxidase [E.C. 1.9.3.1] and b-c1 complex [E.C. 1.10.2.2] and the content of cytochromes b, c + c1 and a + a3 in human skeletal muscle mitochondria from orthopaedic patients (108 women and 68 males), of age ranging between 10 and 50 years, have been analyzed. The activity of cytochrome c-oxidase declines with age both in females and males. The activity of b-c1 complex, which in young females is significantly higher than in young males, declines sharply in females, but not in males, with ageing. These results reveal that the content of active b-c1 complex in muscle mitochondria is specifically controlled by female sex hormones.