Expression and regulation of carnitine palmitoyltransferase-I alpha and -Ibeta genes

Two genes control expression of mitochondrial carnitine palmitoyltransferas e-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 abund ant in the fetus and diminishes at birth. Insulin, thyroid hormone, and fat ty acids regulate expression of CPT-1 alpha in liver, whereas electrical st imulation increases CPT-1 beta and decreases CPT-1 alpha in cardiac myocyte s. Both genes are TATA-less and contain Spl transcription factor binding si tes upstream of the start site of transcription. Multiple transcripts of bo th CPT-1 alpha and CPT-1 beta exist, some of which may have roles in regula ting fatty acid oxidation.