Arrhenius parameters of mitochondrial membrane respiratory enzymes in relation to thermoregulation in endotherms.

The relationship between the body temperature (Tb), the Arrhenius critical temperature (T*), and the apparent activation energy above T* (Ea1), of liver and heart mitochondrial respiratory enzymes from eleven homeothermic and eight heterothermic species was determined using a linear regression analysis. An inverse relation was observed between T* and Ea1 during torpor and hibernation. In all thermoregulatory states, T* decreased with Tb and T* was equal to or below Tb. During torpor Ea1 increased in a linear manner as Tb was lowered. It appears that the above Arrhenius parameters are closely linked to the thermoregulatory state of endotherms and thus may represent an adaptation for function at low Tb's.