Carnitine palmitoyltransferase system and carnitine transporter (CPT system (includes CPT1, CPT2) and CACT (carnitine-acylcarnitine translocase))

The **carnitine palmitoyltransferase system** consists of CPT1 (outer mitochondrial membrane), CACT (inner membrane transporter), and CPT2 (inner mitochondrial membrane enzyme) which, together with the carnitine transporter (OCTN2/SLC22A5), mediate the import, transesterification, and oxidation of long-chain fatty acids in mitochondria. CPT1 catalyzes the conversion of long-chain acyl-CoA to acylcarnitine, CACT shuttles acylcarnitine across the inner membrane in exchange for free carnitine, and CPT2 regenerates acyl-CoA inside the matrix for β-oxidation. Dysregulation or genetic deficiency of any component impairs energy production and is associated with inherited metabolic diseases, myopathies, and involvement in common conditions such as diabetes, cardiovascular disorders, fatty liver, and cancer. Pharmacological modulation of this system is under investigation for various metabolic diseases, but safety and tissue-specific complexity remain important therapeutic challenges.

Other names

Carnitine palmitoyltransferase systemCarnitine shuttleCPT systemCPT1 (isoforms: CPT1A, CPT1B, CPT1C)CPT2Carnitine-acylcarnitine translocase (CACT)

Inhibition of CPT1 blocks mitochondrial fatty acid import and oxidation, shifting energy metabolism to glucose Activation or upregulation enhances FAO and mitochondrial energy generation Inhibition of CPT2 impairs fatty acid β-oxidation CACT inhibition prevents carnitine-acylcarnitine exchange, blocking FA import