Different sensitivity of Zajdela hepatoma mitochondrial ATPase activity to uncouplers in digitonin-treated cells and isolated mitochondria.

Digitonin-treated Zajdela hepatoma cells and rat hepatocytes devoid of almost all cytosol but retaining intact mitochondria were found to represent a suitable system for direct measurement of mitochondrial ATPase activity. The enzyme activity in digitonin-treated Zajdela hepatoma cells in contrast to that of isolated coupled mitochondria was stimulated by uncouplers. No difference in response of mitochondrial ATPase activity to uncouplers in digitonin-treated hepatocytes and isolated liver mitochondria was found. It is concluded that uncoupler-insensitive mitochondrial ATPase activity does not occur in intact in situ tumor mitochondria but is acquired during the isolation of the organelles.