Expression and regulation of carnitine palmitoyltransferase-Iα and -Iβ genes

Two genes control expression of mitochondrial carnitine palmitoyltransferase-1 (CPT-I), the enzyme that catalyzes the primary rate-controlling step in fatty acid oxidation. Two CPT-I isoforms have been found-a "liver" isoform (CPT-1 alpha) expressed in most tissues, but not in Skeletal muscles, and a "muscle" isoform (CPT-1 beta) expressed in muscles and adipocytes. Liver CPT-1 alpha increases dramatically at birth, but heart CPT-1 alpha is abundant in the fetus and diminishes at birth. Insulin, thyroid hormone, and fatty acids regulate expression of CPT-1 alpha in liver, whereas electrical stimulation increases CPT-1 beta and decreases CPT-1 alpha in cardiac myocytes. Both genes are TATA-less and contain Spl transcription factor binding sites upstream of the start site of transcription. Multiple transcripts of both CPT-1 alpha and CPT-1 beta exist, some of which may have roles in regulating fatty acid oxidation.