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Kinetic Properties of Mitochondrial H⁺-Adenosine Triphosphatase in Morris Hepatoma 3924A¹

Institute of Medical Biochemistry and Chemistry, University of Bari, Bari, Italy

A study of kinetic properties of mitochondrial ATPase in Morris hepatoma 3924A is reported. The results show that submitochondrial particles isolated from the tumor tissue exhibited a three-fold increase in both the K_m for ATP hydrolysis and K_i for the competitive inhibitor [ß,-imido]ATP with regard to normal rat liver. Eadie-Hofstee analysis of the kinetics of ATP hydrolysis show that both the high and the low affinity constants for ATP were enhanced in the hepatoma with respect to the rat liver enzyme.

Kinetic analysis of passive proton conduction through the F₀ sector of ATPase does not reveal any difference between Morris hepatoma and rat liver. In Morris hepatoma particles, 50% inhibition of the hydrolase activity required 10 times more oligomycin than in control particles. On the contrary, 50% inhibition of proton conduction occurred in both hepatoma and rat liver particles at the same concentration of oligomycin.

It is concluded that in Morris hepatoma the catalytic process in F₁ and the functional connection between F₁ and F₀ of the ATP synthase are altered with regard to control rat liver.

¹ Supported by grants of the Italian National Research Council, Special Project "Oncology," Contracts 85.02288.44 and 88.00794.44.

² To whom requests for reprints should be addressed, at Institute of Medical Biochemistry and Chemistry, University of Bari, Piazza Giulio Cesare, 70124 Bari, Italy.

Received 1/ 4/88. Revised 6/27/89. Accepted 8/14/89.