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Membranous Effects on Adenosine Triphosphatase Activities of Mitochondria from Rat Liver and Morris Hepatoma 3924A¹

Life Sciences Department, Polytechnic Institute of New York, Brooklyn, New York 11201 [R. L. M., R. M. H.], and Department of Biochemistry, Howard University College of Medicine, Washington, D. C. 20059 [H. P. M.]

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° was observed for the rat liver mitochondrial ATPase, while the hepatoma mitochondrial ATPase revealed a discontinuity at 20.4°. Values for energy of activation of the rat liver and hepatoma mitochondrial ATPase 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 membranes with Triton X-100 resulted in constant and similar values of energy of activation for the ATPases. K_m 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.

¹ Supported by Biomedical Sciences Support Grant RR-07063-09 from the General Research Support Branch, Division of Research Resources, Bureau of Health Professions Education and Manpower Training, NIH.

² Present address: Downstate Medical College, Brooklyn, N. Y. 11203.

Received 2/17/77. Accepted 9/ 6/77.