Beta-oxidation of polyunsaturated fatty acids having double bonds at even-numbered positions in isolated rat liver mitochondria.

beta-Oxidation of polyunsaturated fatty acids was studied with isolated rat liver mitochondria in state 3 or uncoupled conditions. 1. Incubation of mitochondria with docosahexaenoyl-, linolenoyl- or gamma-linolenoylcarnitine resulted in an increase of the absorbance at 340 minus 385 nm. This increased absorbance was due to an accumulation of beta-oxidation intermediates of the polyunsaturated fatty acids, and not to the reduction of nicotinamide nucleotides. 2. Experiments carried out with soluble fractions of liver mitochondria incubated with docosahexaenoyl-CoA and gamma-linolenoyl-CoA indicated that this ultraviolet light-absorption was at least partly caused by acyl-CoA esters having a 2,4(,7)-di(tri)enoyl-CoA structure. 3. The addition of glutamate to mitochondria oxidizing gamma-linolenoylcarnitine decreased the absorbance at 340 minus 385 nm, and simultaneously stimulated respiration. With liver mitochondria isolated from fasted rats, 6 mM glutamate increased the rate of acetoacetate production from gamma-linolenoylcarnitine by 130 and 210% under state 3 and uncoupled conditions, respectively. Glutamate did not have any significant effect on the degradation of oleoylcarnitine. The proposed explanation for these findings is that the glutamate dehydrogenase reaction can function as a source of NADPH for 2,4-dienoyl-CoA reductase. 4. The degradation of gamma-linolenoylcarnitine to ketone bodies was augmented in mitochondria isolated from rats treated with clofibrate or partially hydrogenated marine oil. 5. We conclude that 2,4-dienoyl-CoA reductase is an important auxiliary enzyme in the beta-oxidation of polyunsaturated fatty acids. Induction of this enzyme by clofibrate or by certain high-fat diets increases mitochondrial capacity for the degradation of polyunsaturated fatty acids.