Purification of the medium-chain/long-chain (COT/CPT) carnitine acyltransferase of rat liver microsomes

A procedure for the purification of the rat liver microsomal carnitine octanoyltransferase (COT) that catalyzes the reversible formation of medium-chain and long-chain acylcarnitines from acyl-coenzyme A is described. The K0.5 for L-carnitine is 0.6 mM and the K0.5 for both decanoyl-CoA and palmitoyl-CoA is 0.6 microM. The Vmax with decanoyl-CoA is approximately fourfold greater than the Vmax with palmitoyl-CoA. The enzyme is monomeric, sodium dodecyl sulfate-polyacrylamide gel electrophoresis gives a molecular weight of 50,100, and molecular sieving gives a molecular weight of 54,300. Purified COT does not cross-react with either antimitochondrial carnitine palmitoyltransferase or antiperoxisomal COT antibodies. It also does not form a covalent adduct when incubated with etomoxiryl-CoA. Microsomal COT is a different protein than either mitochondrial carnitine palmitoyltransferase or peroxisomal COT.