INTRAMITOCHONDRIAL CONTROL OF THE OXIDATION OF HEXADECANOATE IN SKELETAL-MUSCLE - A STUDY OF THE ACYL-COA ESTERS WHICH ACCUMULATE DURING RAT SKELETAL-MUSCLE MITOCHONDRIAL BETA-OXIDATION OF [U-C-14]HEXADECANOATE AND [U-C-14]HEXADECANOYL-CARNITINE

1. We describe the acyl-CoA and acyl-carnitine esters which arise from the incubation of well-coupled State 3 rat skeletal-muscle mitochondrial fractions with [U-C-14]hexadecanoate and [U-C-14]hexadecanoyl-carnitine. 2. Acyl-CoA ester intermediates of chain length 16, 14, 12, 10 and 8 carbons were detected. 3. Although incubations were in steady state in respect of oxygen consumption, (CO2)-C-14 production and generation of acid-soluble radioactivity, quantitative analysis of acyl-CoA esters showed that steady state was not achieved in respect of all intermediates. 4. 3-Hydroxyacyl- and 2-enoyl-CoA and -carnitine esters were found under normoxic conditions. 5. Direct measurement of NAD+ and NADH shows that under identical incubation conditions our observations cannot be explained by gross perturbation of the [NAD+]/[NADH] ratio. 6. We hypothesize that there is a small pool of rapidly recycling NAD-channelled between complex I of the respiratory chain and the newly described mitochondrial-inner-membrane-associated beta-oxidation trifunctional enzyme [Uchida, Izai, Orii and Hashimoto (1992) J. Biol. Chem. 267, 1034-1041].