N-(3-Phenylpropionyl)glycine (Phenylpropionylglycine) is an acyl glycine. Acyl glycines are normally minor metabolites of fatty acids. However, the excretion of certain acyl glycines is increased in several inborn errors of metabolism. Acyl glycines are produced through the action of glycine N-acyltransferase which is an enzyme that catalyzes the chemical reaction:acyl-CoA + glycine < - > CoA + N-acylglycineThe detection of phenylpropionylglycine in urine after an oral load of phenylpropionic acid can be used to diagnose deficiency of medium-chain acyl-CoA dehydrogenase, a frequent and treatable metabolic defect.