Membrane microenvironment regulation of carnitine palmitoyltranferases I and II

CPT (carnitine palmitoyltransferase) 1 and CPT2 regulate fatty acid oxidation. Recombinant rat CPT2 was isolated from the soluble fractions of bacterial extracts and expressed in Escherichia coli. The acyl-CoA chain-length-specificity of the recombinant CPT2 was identical with that of the purified enzyme from rat liver mitochondrial inner membranes. The K_m for carnitine for both the mitochondrial preparation and the recombinant enzyme was identical. In isolated mitochondrial outer membranes, cardiolipin (diphosphatidylglycerol) increased CPT1 activity 4-fold and the K_m for carnitine 6-fold. It decreased the K_i for malonyl-CoA inhibition 60-fold, but had no effect on the apparent K_m for myristoyl-CoA. Cardiolipin also activated recombinant CPT2 almost 4-fold, whereas phosphatidylglycerol, phosphatidylserine and phosphatidylcholine activated the enzyme 3-, 2- and 2-fold respectively. Most of the recombinant CPT2 was found to have substantial interaction with cardiolipin. A model is proposed whereby cardiolipin may hold the fatty-acid-oxidizing enzymes in the active functional conformation between the mitochondrial inner and outer membranes in conjunction with the translocase and the acyl-CoA synthetase, thus combining all four enzymes into a functional unit.