On the capacity of the β‐oxidation of palmitate and palmitoyl‐esters in rat liver mitochondria

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Abstract
The .beta.-oxidation of palmitate, palmitoyl-CoA and palmitoyl-L-carnitine proceeded at a high rate in isolated rat liver mitocondria. A high concentrations (100 nmol/mg protein) the oxidation of palmitate and palmitoyl-CoA was only partly carnitine dependent. All substrates were most rapidly oxidized in the presence of oxatoacetate and state 3 conditions. Succinate inhibited .beta.-oxidation especially in state 4 conditions. .beta.-Oxidation was faster in hypotonic than in isotonic medium both in state 3 and in state 4 conditions. Hypertonicity inhibited .beta.-oxidation. The initial formation of palmitoyl-CoA from palmitate, CoA and ATP was faster than the oxidation of palmitate under identical conditions. The presence of bovine serum albumin inhibited the .beta.-oxidation, especially with palmitoyl-CoA or free palmitate as the substrates. Mitochondria contain a palmitoyl-CoA hydrolase which may influence the available intramitochondrial palmitoyl-CoA. The present results demonstrate no single rate limiting step in the .beta.-oxidation in vitro. Both the NADH/NAD ratio, competition for the respiratory chain, the level of ADP, binding of palmitoyl-CoA to extramitochondrial protein, and possibly intramitochondrial hydrolysis of palmitoyl-CoA all seem to influence the rate of .beta.-oxidation in vitro. In vivo the most important factor may be the availability of acyl-CoA to the outer carnitine palmitoyl-transferase of the mitochondria.

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