The carnitine acyltransferases: modulators of acyl-CoA-dependent reactions

Carnitine and carnitine acyltransferases were thought to be merely a mechanism for the rapid transfer of activated long-chain fatty acids into the mitochondrion for beta-oxidation [1], until enzymologists came along. By kinetic, physical and localization studies, eight different mammalian carnitine acyltransferases have been characterized (reviewed in [2,3]). Of these, five have been cloned and sequenced. The carnitine:acylcarnitine exchange carrier, first characterized in mitochondria [4,5], has now been demonstrated immunologically in peroxisomal membranes too [6]. This cell-wide carnitine system consisting of at least six proteins linking at least four intracellular pools of acyl-CoA that supply a multitude of lipid metabolic pathways is clearly more complex than was first thought. In this article, I describe the location and properties of the components to show how they can modulate acyl-CoA-dependent reactions in the cell.