Figure 2. Measurement of coupled CI-CIII and CII-CIII activities from young, middle aged and old WT and dwarf mouse heart mitochondria. Coupled enzyme activities were measured spectrophotometrically as described in Methods. All activity results are the average of 4 assays from the pooled samples ± SEM for each age group. Citrate synthase activities were used to normalize mitochondrial proteins. Activities for young (4-5 months), middle-aged (10-12 months), and old (20-26 months) WT and dwarf heart CI-III and CII-III are plotted as follows: (A) CI-CIII coupled activity. Coefficients of variance for WT and dwarf were 3.4% and 6.5% (young), 9% and 10.2% (middle-age), and 4.1% and 2.2% (old), respectively. (B) CII-CIII coupled activity. Coefficients of variance for WT and dwarf were 7.2% and 11.3% (young), 6.3% and 7.7% (middle-age), and 7.7% and 15.4% (old), respectively. * - p<0.05 compared to young, ** - p<0.001 compared to young, † - p<0.05 compared to middle-aged, ‡ - p<0.05 compared to WT, and ‡‡ - p<0.001 compared to WT.