The mechanism of inhibition by fluoride of mitochondrial fatty acid oxidation

Abstract

The following evidence is presented in favour of the old hypothesis that F − inhibition of fatty acid oxidation in intact, coupled rat-liver mitochondria is due to an accumulation of pyrophosphate in the mitochondrial matrix: 1. 1.Addition of fatty acid to mitochondria oxidizing malate in the presence of F − initially causes an increased rate of O 2 uptake, followed by a gradual decrease, indicating the accumulation of an inhibitor as a result of fatty acid oxidation. 2. 2. This inhibition is only found when the fatty acid substrate is activated in the mitochondrial matrix. 3. 3. The matrix acyl-CoA synthetase (acid:CoA ligase (AMP), EC 6.2.1.3) is strongly inhibited by pyrophosphate. 4. 4. Mitochondrial pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) is inhibited by F − and is localized mainly in the matrix. 5. 5. The mitochondrial inner membrane is impermeable to pyrophosphate. 6. 6. Pyrophosphate accumulates in mitochondria oxidizing fatty acid in the presence of fluoride. Oxidation of fatty acids by uncoupled mitochondria in the absence of inorganic phosphate also leads to pyrophosphate accumulation when F − is added, showing that under these conditions too, an ATP-dependent acyl-CoA synthetase is active.