CPT1B, a member of the carnitine/choline acetyltransferase family, is the rate-controlling enzyme of the long-chain fatty acid beta-oxidation pathway in muscle mitochondria. This enzyme is required for the net transport of long-chain fatty acyl-CoAs from the cytoplasm into the mitochondria. Multiple transcript variants encoding different isoforms have been found for this gene, and read-through transcripts are expressed from the upstream locus that include exons from this gene.

Analysis of CPT1B cDNA sequences revealed the presence of an untranslated 5-prime exon and differential processing of introns 13 and 19. The alternative splicing of intron 13 caused an in-frame deletion leading to a protein smaller by 10 amino acids.