Oxidation of long chain fatty acids by rat liver mitochondria.

Long chain fatty acids are oxidized by rat liver mitochondria provided that endogenous adenosine triphosphate is not depleted. If endogenous ATP is depleted, e.g. by Z,&dinitrophenol, external ATP as well as carnitine is required for fatty acid oxidation. Atractyloside does not block this reaction in media containing orthophosphate buffer. Oligomycin can substitute for carnitine, but the oligomycin-dependent route is inhibited by atractyloside. These experimental situations localize two ATP-dependent fatty acid-activating systems, one of which is linked to carnitine. The dinitrophenol-insensitive, GTP-specific fatty acyl coenzyme A synthetase is active only in the absence of orthophosphate. Inhibition of oxidation of fatty acids by atractylate in phosphate-free media is not relieved with oligomycin or carnitine.