Figure 6. Measurement of coupled mitochondrial ETC complex activities from young, middle aged and old WT and dwarf mouse quadriceps muscle mitochondria. CI-III and CII-III 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 quadriceps CI-III and CII-III are plotted as follows: (A) CI-CIII coupled activity. Coefficients of variance for WT and dwarf were 3.1% and 2.5% (young), 2.8% and 2.5% (middle-age), and 6.5% and 3.1% (old), respectively. (B) CII-CIII coupled activity. Coefficients of variance for WT and dwarf were 2.2% and 4.3% (young), 9.2% and 6.8% (middle-age), and 10.5% and 13.3% (old), respectively. * - p<0.05 compared to young, ** - p<0.001 compared to young, †† - p<0.001 compared to middle-aged, and ‡ - p<0.05 compared to WT.