acylcarnitine

Acylcarnitine is an ester of carnitine with a fatty acid, forming a family of molecules that participate in the transport of fatty acyl groups into mitochondria for beta-oxidation. They arise when fatty acyl-CoA is converted to acylcarnitine by carnitine palmitoyltransferase I (CPT I) on the outer mitochondrial membrane, allowing translocation across the inner membrane via the carnitine–acylcarnitine translocase, where CPT II reconverts it to acyl-CoA for oxidation.

Acylcarnitines vary by fatty acid chain length, yielding short-, medium-, and long-chain species. Common examples include acetylcarnitine (C2), propionylcarnitine (C3), and palmitoylcarnitine (C16). They can be measured in blood or dried blood spots and serve as useful biomarkers of mitochondrial fatty acid oxidation and related metabolic pathways.

Clinically, acylcarnitine profiling by tandem mass spectrometry is a standard component of newborn screening and is employed to diagnose fatty acid oxidation disorders and other metabolic diseases. Characteristic patterns help distinguish conditions such as carnitine palmitoyltransferase I deficiency, carnitine palmitoyltransferase II deficiency, very long-chain acyl-CoA dehydrogenase deficiency (VLCAD), and medium-chain acyl-CoA dehydrogenase deficiency (MCAD). Elevated long-chain acylcarnitines with low free carnitine can indicate transporter or oxidation defects, while accumulations of specific short- or medium-chain species point to other enzymatic blocks.

Beyond diagnostics, acylcarnitines are studied as indicators of metabolic flux and mitochondrial function, reflecting the balance between fatty acid availability, transport, and oxidation.