CPT1 is an integral membrane protein that associates with the mitochondrial outer membrane through transmembrane regions in the peptide chain. Both the N- and C-terminal domains are exposed to the cytosolic side of the membrane.[4]
Three isoforms of CPT1 exist in mammalian tissues. The liver isoform (CPT1A or CPTI-L) is found throughout the body on the mitochondria of all cells except for skeletal muscle cells and brown adipose cells.[5][6] The muscle isoform (CPT1B or CPTI-M) is highly expressed in heart and skeletal muscle cells and brown adipose cells.[4][5][6] A third isoform, the brain isoform (CPT1C), was isolated in 2002. It is expressed predominantly in the brain and testes. Little is known about CPT1C.[7][8]