Carnitine palmitoyltransferase: characterization of a labile detergent-extracted malonyl-CoA-sensitive enzyme from rat liver mitochondria.

Rat liver mitochondria were preextracted with Triton X-100 in the absence of salts to remove malonyl-CoA-insensitive carnitine palmitoyltransferase. From the remaining membrane residues a malonyl-CoA-sensitive enzyme was solubilized with octyl glucopyranoside in the presence of KCl. Significant enzyme activity, [2-14C]malonyl-CoA binding and malonyl-CoA inhibition of this enzyme was present only after removal of detergent by precipitation with poly(ethylene glycol). The enzyme activity was rapidly lost in the solubilized form. High concentrations of glycerol protected the enzyme. The alkylating irreversible inhibitor, S-(4-bromo-2,3-dioxobutyl)-CoA, strongly inhibited the malonyl-CoA-sensitive enzyme in the membrane residues. The enzyme was protected against this inhibitor by malonyl-CoA and palmitoyl-CoA. The more loosely membrane-bound malonyl-CoA-insensitive enzyme failed to bind malonyl-CoA, was stable in the presence of detergents and was not inhibited by S-(4-bromo-2,3-dioxobutyl)-CoA. It is suggested that two different carnitine palmitoyltransferase proteins exist in the inner mitochondrial membrane and that the detergent-labile malonyl-CoA-sensitive enzyme is the less easily extracted of the two.