Studies on the effects of saturated and unsaturated short-chain monocarboxylic acids on the energy metabolism of rat liver mitochondria.

The effect of eight branched-chain amino acid metabolites, four metabolites from the beta-oxidation, and the unphysiologic acid 4-pentenoic acid on the oxygen consumption rate of liver mitochondria oxidizing pyruvate, 2-oxo-glutarate, and L-palmitoylcarnitine has been investigated. The 12 metabolites are: propionic, isobutyric, 2-Me-butyric, isovaleric, acrylic, Me-acrylic, tiglic, Me-crotonic, butyric, hexanoic, crotonic, and 2-hexenoic acids. The oxidation rate of pyruvate was strongly inhibited by propionic, 4-pentenoic, and isovaleric acids at 0.1, 0.1, and 1.0 mM, respectively. With 2-oxo-glutarate as substrate, the oxygen consumption rate was strongly inhibited at 0.1 mM of propionic, 4-pentenoic, and isovaleric acids. The L-palmitoyl-carnitine oxidation rate was very strongly inhibited by 0.1 mM 4-petenoic acid, whereas butyric and hexanoic acids exerted a moderate inhibition at 0.1 mM. Propionic acid inhibited L-palmitoylcarnitine oxidation slightly at 1.0 mM. It is argued that propionyl-CoA and isovaleryl-CoA inhibit pyruvate and 2-oxo-glutarate dehydrogenases directly, and the significance of the results for ketotic episodes in organic acidurias is discussed.