Intramitochondrial L-carnitine can also be transesterified to O-acetylcarnitine by carnitine O-acetyltransferase (EC 2.3.1.7) using acetyl-CoA, the product of fatty acid β-oxidation (see pathway fatty acid β-oxidation I). O-acetylcarnitine can then leave the mitochondrion via the carnitine-acylcarnitine translocase. Similarly, coenzyme A derivatives of short-chain fatty acids can also be trans-esterifed by this enzyme and leave the mitochondrion. All of these reversible acylations provide a mechanism for modulation of intracellular coenzyme A and acyl-CoA concentrations.