Figure 2.

Body mass dependence of mitochondrial coupling efficiency varies with ATP synthesis levels. (a) Relationships between mitochondrial efficiency (ATP/O ratios) and the rates of ATP synthesis in muscle mitochondria from mammals of different body mass. Red symbols illustrate the nonlinearity of the relationships. Values are means from n independent mitochondrial preparations; (n) is given alongside the name of the species. Error bars (s.d.) are omitted for clarity but were on average 10% for maximal ATP/O ratio (ranging from 4% in pygmy mice to 30% in boar) and 25% for maximal ATP synthesis rate (ranging from 9% in pygmy mice to 46% in sheep). (b) Relationships between ATP/O ratio calculated for a given ATP synthesis rate and body mass are: at 400 nmol ATP min⁻¹ mg⁻¹ ATP/O = 1.46 × mass^0.038 (black circles; r² = 0.73; F_1,8 = 9.91; p < 0.05); at 200 nmol ATP min⁻¹ mg⁻¹, ATP/O = 1.01 × mass^0.050 (white circles; r² = 0.67; F_1,10 = 10.41; p < 0.01); at 100 nmol ATP min⁻¹ mg⁻¹, ATP/O = 0.60 × mass^0.071 (dark triangles; r² = 0.78; F_1,10 = 15.58; p < 0.01); at 50 nmol ATP min⁻¹ mg⁻¹, ATP/O = 0.32 × mass^0.091 (grey triangles; r² = 0.84; F_1,10 = 20.57; p < 0.01); at 10 nmol ATP min⁻¹ mg⁻¹, ATP/O = 0.07 × mass^0.118 (white triangles; r² = 0.88; F_1,10 = 27.99; p < 0.001). Values are means ± s.d. (Online version in colour.)