Changes in the respiratory chain complexes activities and in the mitochondrial DNA content during ageing in D. subobscura.

The time course (age 0-8 weeks) of the enzyme activities of respiratory chain complexes I, III and IV and of citrate synthase, and the cell mitochondrial/nuclear DNA content ratio were studied in Drosophila subobscura. The activities of the three respiratory complexes decreased with age, but with different kinetics. The activities of complexes I and III remained nearly stable between weeks 0 and 3 (falling by 6% and 15%, respectively), and then gradually decreased; after 8 weeks residual activities were about 50% of the initial value for complexes I and III. The activity of complex IV fell in the first week, decreasing continually to week 8, where residual activity was 30% of the initial value. No significant age-related change in citrate synthase activity was observed. Mitochondrial DNA (measured by mitDNA/nucDNA) increased linearly up to week 5 (2.6-fold) and then dropped by 40% in week 6 though it remained higher than initial values.