Abstract
Oxidation of palmitate by rat skeletal muscle mitochondria was determined polarographically and radiochemically under state 3 conditions. Maximal oxidation rate is reached at 4 μ m palmitate, palmitoyl-CoA, or palmitoyl- l-carnitine. At palmitoyl-CoA concentrations higher than 30 μ m oxidation is inhibited. At limiting substrate concentrations as used in polarographic experiments palmitate is totally degraded to CO 2. At higher concentrations the palmitate molecule is only partially degraded, due to the accumulation of intermediates. Citric acid cycle intermediates, especially 2-oxoglutarate, accumulate during oxidation of palmitate in the presence of malate. It is suggested that this accumulation is stimulated by dicarboxylate exchange. The rate of formation of 14CO 2 and 14C-labeled perchloric acid-soluble products is higher from [1- 14C]palmitate than that from [ U- 14C]palmitate. This difference, which is enhanced by higher carnitine concentrations indicates incomplete oxidation during the β-oxidation in state 3. The simultaneous determination of 14CO 2 production and 14C-labeled perchloric acid-soluble products appears to be a more accurate and sensitive method for measuring 14C-fatty acid oxidation than that of 14CO 2 production alone.
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