Membranous effects on adenosine triphosphatase activities of mitochondria from rat liver and Morris hepatoma 3924A.

Adenosine triphosphatase (ATPase) activities of sonically prepared submitochondrial particles of rat liver and Morris Hepatoma 3924A were compared as a function of changes in temperature. On Arrhenius plots, a discontinuity at 18 degrees was observed for the rat liver mitochondrial ATPase, while the hepatoma mitochondrial ATPase revealed a discontinuity at 20.4 degrees. Values for energy of activation of the rat liver and hepatoma mitochondrial ATPases were comparable below the break (34.5 and 35.5 kcal/mole, respectively) and above the break (11.6 and 9.2 kcal/mole, respectively). Solubilization of the mitochondrial membrances with Triton X-100 resulted in constant and similar values of energy of activation for the ATPases Km values of hepatoma and rat liver mitochondrial ATPases for adenosine triphosphate were similar in both the membrane-bound and solubilized states. The lack of uncoupler-stimulated ATPase activity in hepatoma mitochondria is apparently not due to membranous effects on the affinity of the ATPase for adenosine triphosphate.