Activation energies of different mitochondrial enzymes: Breaks in Arrhenius plots of membrane-bound enzymes occur at different temperatures

A series of mitochondrial enzymes exhibit breaks in Arrhenius plots from low to high activation energies upon temperature decrease. All membrane-bound enzymes tested except cytochrome c oxidase have shown these transitions, while soluble matrix enzymes (malic dehydrogenase and fumarase) did not have breaks or they had different characteristics. Triton-X-100 which solubilizes the mitochondrial membrane, induces a straightening of the plot for ATPase. The observation that the breaks in the Arrhenius plots for membranous enzymes fall at different temperatures suggests caution in their correlation with phase transitions of membrane phospholipids.