carnitineacylcarnitine

Carnitineacylcarnitine is not a standard term in biochemistry; the compounds it would describe are typically called acylcarnitines. Acylcarnitines are esters formed when carnitine reacts with fatty acyl groups, resulting in a molecule that carries a fatty acyl moiety on the carnitine backbone. They exist in various chain lengths, from short-chain to very long-chain acylcarnitines, reflecting different fatty acid sources and metabolic pathways.

Biosynthesis and role in metabolism: Acylcarnitines arise mainly through the action of carnitine palmitoyltransferase enzymes (CPT1 on the outer mitochondrial membrane and CPT2 on the inner membrane). CPT1 transfers the acyl group from fatty acyl-CoA to carnitine, forming acylcarnitine, which is shuttled across the inner mitochondrial membrane by the carnitine–acylcarnitine translocase. CPT2 then re-forms the fatty acyl-CoA inside the mitochondrial matrix for beta-oxidation. This transport system enables long-chain fatty acids to access mitochondrial enzymes for energy production. Acylcarnitines also appear in amino acid catabolism and other metabolic processes, contributing to cellular acetyl-CoA and energy balance.

Clinical and analytical relevance: The acylcarnitine profile is used clinically to screen for and monitor fatty acid oxidation disorders and other metabolic diseases. Abnormal levels of specific acylcarnitines in blood or plasma can indicate CPT deficiencies, carnitine deficiency, or impaired beta-oxidation. Newborn screening programs often employ tandem mass spectrometry to measure a panel of acylcarnitines for early detection of metabolic conditions. Analytical methods typically rely on mass spectrometry, using dried blood spots or plasma samples.

See also: carnitine, CPT1, CPT2, CACT, acylcarnitine profiles.