Temperature dependence of the coupling efficiency of rat liver oxidative phosphorylation: role of adenine nucleotide translocator.

We have reinvestigated the temperature dependence of the coupling efficiency of energy conversion in isolated rat liver mitochondria. We observed that respiratory control increased with temperature. Moreover, in the same conditions, the ATP/O ratio increased. The measurement of the control coefficients of adenine nucleotide translocator on respiratory and ATP synthesis rates showed that at 28 degrees C, this translocator exerted the same control (about 0.5) on both fluxes. At 4 degrees C, it no longer exerted control on respiratory flux when its control on ATP synthesis flux came close to 1. In addition, ATP/O ratio values and control coefficients on ATP synthesis flux were bound by a unique linear relationship irrespective of temperature. In conclusion, the decrease in ATP/O ratio with temperature is a direct consequence of an increase in the kinetic control exerted by the adenine nucleotide translocator on ATP synthesis.