Propionyl-CoA is an intermediate in the metabolism of propanoate. Propionic aciduria is caused by an autosomal recessive disorder of propionyl coenzyme A (CoA) carboxylase deficiency (EC 6.4.1.3). In propionic aciduria, propionyl CoA accumulates within the mitochondria in massive quantities; free carnitine is then esterified, creating propionyl carnitine, which is then excreted in the urine. Because the supply of carnitine in the diet and from synthesis is limited, such patients readily develop carnitine deficiency as a result of the increased loss of acylcarnitine derivatives. This condition demands supplementation of free carnitine above the normal dietary intake to continue to remove (detoxify) the accumulating organic acids. Propionyl-CoA is a substrate for Acyl-CoA dehydrogenase (medium-chain specific, mitochondrial), Acetyl-coenzyme A synthetase 2-like (mitochondrial), Propionyl-CoA carboxylase alpha chain (mitochondrial), Methylmalonate-semialdehyde dehydrogenase (mitochondrial), Trifunctional enzyme beta subunit (mitochondrial), 3-ketoacyl-CoA thiolase (peroxisomal), Acyl-CoA dehydrogenase (long-chain specific, mitochondrial), Malonyl-CoA decarboxylase (mitochondrial), Acetyl-coenzyme A synthetase (cytoplasmic), 3-ketoacyl-CoA thiolase (mitochondrial) and Propionyl-CoA carboxylase beta chain (mitochondrial).