Long-chain fatty acyl-CoA synthetase of rat adrenal microsomes. Effect of ACTH and epinephrine

Acyl-CoA synthetase activity with various long-chain fatty acid substrates and its kinetic properties were measured in rat adrenal microsomes. The apparent Michaelis constants ( K m ) for substrate fatty acids increased in the order eicosa-8,11,14-trienoic acid š α-linolenic acid < linoleic acid < palmitic acid. The maximum velocities with these fatty acids decreased in the order linoleic > α-linolenic > eicosa-8,11,14-trienoic acid >palmitic acid. The synthesis of radioactivity palmitoyl-CoA, linoleyl-CoA, α-linolenyl-CoA and eicosa-8,11,14-trienoyl-CoA from the respective radioactive substrates decreased in the presence of all the other fatty acids mentioned above. These effects were inversely correlated with their apparent K m values. These results support the idea of a single long-chain fatty acyl-CoA synthetase in the adrenal microsomal fraction for the acid tested. After testing the influence of different hormones, it was shown that the administration of epinephrine, ACTH and dexamethasone caused a significant decrease in the activity of the long-chain fatty acid-CoA synthetase. This inhibition is independent of the one produced by the same hormones on the desaturation of linoleic to γ-linolenic acid.