FIGURE 1.

The effect of temperature on the mitochondrial oxidative phosphorylating efficiency. (A) The rates of ATP synthesis and oxygen consumption were determined at 20°C (white circles), at 25°C (gray circles), and at 30°C (black circles) in the mitochondria isolated from the liver of toad and respiring on succinate. Mitochondrial fluxes were titrated with increasing concentrations of ADP in the presence of glucose and hexokinase (see section “Materials and Methods” for more details). Values are means ± SEM for N = 5 independent mitochondrial preparations. (B) The coupling efficiency calculated at the highest common ATP synthesis rate between the three temperatures (13.6 nmol ATP min^–1 mg^–1 protein). Shortly, oxygen consumption rates were calculated at this highest common ATP synthesis rate by using individual linear relation curves. Then, the resulting effective ATP/O ratios were calculated at 20°C (white bars), at 25°C (gray bars), and at 30°C (black bars). The values are means ± SEM for N = 5 independent mitochondrial preparations. * and † mean significantly different from 20 and 25°C, respectively (p < 0.05).