Effects of Temperature, pH, and CO₂ Tension on the Metabolism of Isolated Hepatic Mitochondria of the Desert Iguana, Dipsosaurus dorsalis

Abstract

Mitochondria were isolated from the liver of the desert iguana, Dipsosaurus dorsalis. The kinetics (Km, Vmax) of succinate oxidation by these mitochondria were determined at 25 C and 40 C over a range of pH values (6.5-7.5) and CO₂ tensions (0.2-41 torr). Mitochondrial succinate oxidation was very closely described by Michaelis-Menten kinetics. Vmax varied directly with temperature but was not affected by variation of either pH or PCO₂. Apparent Km for succinate was affected by pH and PCO₂ as well as temperature, varying directly with pH and PCO₂ but inversely with temperature. The effects of temperature on Km for succinate were minimized when mitochondria were incubated in media whose pH and PCO₂ approximated in vivo intracellular values. The Q10 values were calculated for three different acid-base regulatory patterns over a wide range of substrate concentrations. The data support the hypothesis that the desert iguana's normal acid-base regulatory pattern serves to minimize the effect of temperature on mitochondrial metabolism. The results, however, cannot be explained solely in terms of temperature/acid-base effects on the ionization state of proteinbound dissociable groups.