Inter-tissue and inter-species characteristics of the mitochondrial carnitine palmitoyltransferase enzyme system

Properties of the carnitine palmitoyltransferase (EC 2.3.1.21) (CPT) enzyme system were compared in isolated mitochondria from a range of tissues in rodents, monkey, and man. Common features were as follows: (a) while membrane-bound, CPT I, but not CPT II, was inhibited reversibly by malonyl-coenzyme A (CoA) and irreversibly by CoA esters of certain oxirane carboxylic acids; (b) the detergent, Tween-20, readily solubilized CPT II in active form while leaving CPT I membrane associated and catalytically functional; (c) octyl glucoside and Triton X-100 released active CPT II but caused essentially complete loss of CPT I activity. Use of [³H]tetradecylglycidyl-CoA, a covalent ligand for CPT I, yielded estimates of the enzyme's monomeric molecular size: ~86 kDa in non-hepatic tissues and ~90-94 kDa in liver, depending upon species. A polyclonal antibody to purified rat liver CPT II recognized a single protein in each tissue; its apparent molecular mass was ~70 kDa in all rat tissues and ~68 kDa in all mouse tissues as well as monkey and human liver. On Northern blot analysis a rat liver CPT II cDNA probe detected a single ~2.5-kilobase mRNA in all rat and mouse tissues examined. The following points are emphasized. First, CPT I and II are different proteins. Second, within a species CPT II, but not CPT I, is probably conserved across tissue lines. Third, slight variations in size of both enzymes were found in different species, although, at least in the case of CPT II, significant amino acid identity exists among the various isoforms. Fourth, CPT I, unlike CPT II, requires membrane integrity for catalytic function. Finally, the strategic use of detergens provides a simple means of discriminating between the two enzyme activities.