ATPase activity of mitochondria isolated from Ehrlich ascites carcinoma and hepatoma BW7756 declines over time when assayed in the absence of added magnesium ions. In contrast, rat liver mitochondria when assayed in the presence or absence of added magnesium ions or the tumor mitochondria when assayed in the presence of added magnesium ions, maintain a constant level of ATPase activity when incubated in 0.25 M sucrose at 0o. Studies monitoring loss of endogenous magnesium from normal and tumor mitochondria reveal that the tumor mitochondria are much more leaky to magnesium, and that this loss of endogenous magnesium can be effectively blocked by addition of bovine serum albumin (albumin). Tumor mitochondria when isolated in the absence of albumin contain more than twice the levels of free fatty acids than rat liver mitochondria, and exhibit only a slight to moderate stimulation of ATPase activity in response to 2,4-dinitrophenol. In contrast, when tumor mitochondria are isolated in the presence of albumin, the resultant mitochondria contain lower levels of free fatty acids, and latent ATPase activity can be greatly stimulated by addition of 2,4-dinitrophenol. Adenine nucleotide translocase activity of tumor mitochondria is enhanced more than 5-fold in mitochondria isolated in the presence of albumin compared to tumor mitochondria isolated in the absence of albumin. In all assays, the maximum specific activity for tumor mitochondrial nucleotide translocation was less than 50% of that exhibited by rat liver mitochondria.
The results in this paper strongly indicate (a) the low uncoudler-stimulated ATPase activity in mitochondria isolated from Ehrlich ascites carcinoma and hepatoma BW7756 cells is due to high levels of endogenous free fatty acids that are inhibiting adenine nucleotide translocation, while simultaneously inducing the loss of endogenous magnesium; and (b) that when tumor mitochondria are isolated and incubated in the presence of albumin the high levels of uncoupler stimulation observed are due to the prevention of mitochondrial magnesium loss and activation of the adenine nucleotide translocation.