Effects of long‐chain fatty acids on the inhibition by antimycin of respiration in hepatocytes and isolated mitochondria from rat liver

A previous study [Berry, M. N., Gregory, R. B., Grivell, A. R. & Wallace, P. G. (1983) Eur. J. Biochem. 131, 215–222] suggested that long‐chain fatty acid (palmitate) oxidation by hepatocytes was less sensitive than short‐chain fatty acid (hexanoate) oxidation to inhibition by a given concentration of antimycin. Re‐examination of this phenomenon showed that palmitate oxidation by hepatocytes could be depressed by antimycin to the same degree as other NAD+‐linked substrates, only if the concentration of the inhibitor was raised 2–4‐fold. The presence of palmitate also reduced the sensitivity to antimycin of hepatocytes metabolizing lactate or pyruvate. Over the range of fatty acids tested, butyrate (C4) to stearate (C18), only long‐chain (> C10) fatty acids endowed cells with decreased sensitivity towards antimycin. 2‐Bromopalmitate, a non‐metabolizable fatty acid, and inhibitor of fatty acid oxidation, also decreased the inhibitory effect of antimycin in cells, suggesting that long‐chain fatty acids per se rather than their metabolites, reverse the inhibition by antimycin. Moreover, another inhibitor of fatty acid oxidation, 2‐tetradecylglycidic acid, did not diminish the effects of palmitate. Succinate oxidation in isolated mitochondria that had been inhibited by a low concentration of antimycin could be restored by subsequent addition of palmitate or other long‐chain fatty acids such as dodecanoate, tetradecanoate and oleate under conditions where fatty acid oxidation was prevented. 2‐Bromopalmitate, likewise partially restored antimycin‐depressed succinate oxidation. This amelioration of antimycin inhibition was counteracted by the addition of more antimycin and was not seen upon addition of defatted bovine serum albumin, palmitoylcarnitine or octanoate. The total amount of antimycin bound to mitochondria was not affected by the presence of palmitate. The data suggest that long‐chain fatty acids are able to interact with the mitochondrial inner membrane in a manner which can relieve the inhibitory effect of antimycin, whether the antimycin is added to the cell or mitochondrial suspension before or after fatty acid addition.