Intermediates of myocardial mitochondrial beta-oxidation: possible channelling of NADH and of CoA esters

Adult rat heart mitochondria were isolated and incubated with U-14C]hexadecanoyl-CoA or unlabelled hexadecanoyl-CoA. The accumulating CoA and carnitine esters and NAD+]/NADH] ratio were measured by HPLC or tandem mass spectrometry. Despite minimal changes in the intramitochondrial NAD+]/NADH] ratio, 2, 3-unsaturated and 3-hydroxyacyl esters were observed as well as saturated acyl-CoA and acylcarnitine esters. In addition to acetylcarnitine, significant amounts of butyryl-, hexanoyl-, octanoyl- and decanoylcarnitines were detected and measured. Rat myocardial beta-oxidation is subject to control at the level of 3-hydroxyacyl-CoA dehydrogenase but this control is not due to a simple lack of oxidised NAD. We hypothesise a pool of NAD in contact between the trifunctional protein of beta-oxidation and complex I of the respiratory chain, the turnover of which is responsible for some of the control of beta-oxidation flux. In addition, short- and medium-chain acylcarnitine esters were detected whereas only small amounts of long-chain acylcarnitines were present. This may imply the presence of a mitochondrial carnitine octanoyl transferase or may reflect channelling of long-chain CoA esters so that they are not available for carnitine palmitoyl transferase II activity.