The mechanism of inhibition by fluoride of fatty acid oxidation in uncoupled mitochondria

Abstract

Fatty acid oxidation by intact uncoupled rat-liver mitochondria is inhibited by F −. This is due primarily to the inhibition by fluoride of the mitochondrial pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1 ). Pyrophosphate was found to accumulate both in the mitochondrial matrix and in the incubation medium. When low concentrations of P i are present, the internal pyrophosphate concentration rises to such an extent that the matrix acyl-CoA synthetase (acid: CoA ligase (AMP), EC 6.2.1.3) is inhibited. In the absence of added phosphate the rate of fatty acid oxidation decreases abruptly a few minutes after addition of fluoride. This is caused by depletion of endogenous phosphate, necessary for substrate-level phosphorylation. The internal pyrophosphate concentration decreases after fatty acid oxidation has become inhibited, whereas the pyrophosphate content of the medium continues to rise due to a leakage of pyrophosphate from the mitochondria. The initial rate of palmitate oxidation in the presence of fluoride is only slightly lower than in its absence, indicating that the GTP-dependent acyl-CoA synthetase does not play an important role in the activation of fatty acids by uncoupled mitochondria.