Tightly coupled mitochondria isolated from Ehrlich ascites tumor cells contain a latent adenosine triphosphatase (ATPase) that is stimulated by a range of dinitrophenol concentrations up to 0.5 mm. Maximal uncoupler-stimulated ATPase activity is approximately 60% of that found with rat liver mitochondria and is inhibited by oligomycin and by atractyloside.

Rapid rates of ATPase activity accompany the accumulation of Ca2+ by ascites tumor mitochondria in an adenosine triphosphate-supported system. In contrast to Ca2+, Mg2+ is unable to induce ATPase activity in intact mitochondria but can in sonically disrupted preparations. Prolonged incubation of the ascites mitochondria with Ca2+ does not lead to irreversible ATPase, swelling, or spontaneous release of the accumulated Ca2+, events typical of rat liver mitochondria.

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This study was supported by a grant from the Australian Capital Territory Cancer Society.

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