Rates of Oxidation of Different Fatty Acids by Isolated Rat Liver Mitochondria

The oxidation rates for palmitic, stearic, oleic, and linoleic acids as their albumin complexes and for caprylic, butyric, and acetic acid as their potassium salts with isolated rat liver mitochondria were studied in a system where it had previously been demonstrated that the respiratory chain and the coupling of phosphorylation to oxidation is intact even at high concentrations of long chain fatty acids. Results were obtained which apparently fitted the Michaelis-Menten equation. The values of Km decreased with increasing length of the carbon chain. Of the long chain fatty acids, linoleic acid has the lowest constant. Vmax for long chain fatty acids was highest for linoleic acid, but this value was not as high as those of short chain fatty acids. However, if different substrates were compared in terms of the product nVmax, where n is the number of carbon atoms in the fatty acid, linoleic acid shows as high values as short chain fatty acids. The possibility is discussed that linoleic acid has the highest affinity for the mitochondrial fatty acid oxidation system and that it is oxidized at the fastest rate of the long chain fatty acids studied. Implications of this findings for previously observed differences in fatty acid metabolism in vivo, explainable by increased linoleic acid oxidation, are considered.