Hydroxyphenylacetylglycine is an acylglycine. Acylglycines are normally minor metabolites of fatty acids. However, the excretion of certain acylglycines is increased in several inborn errors of metabolism. In certain cases the measurement of these metabolites in body fluids can be used to diagnose disorders associated with mitochondrial fatty acid beta-oxidation. Acyl glycines are produced through the action of glycine N-acyltransferase (EC 126.96.36.199) which is an enzyme that catalyzes the chemical reaction: acyl-CoA + glycine ↔ CoA + N-acylglycine. Hydroxyphenylacetylglycine is an endogenous human metabolite. It can be originated from the metabolism of tyramine, itself is a monoamine compound derived from the amino acid tyrosine. Hydroxyphenylacetylglycine can also be derived from the metabolism of 3,4-dihydroxyphenylalanine (L-DOPA). In the metabolism of tyrosine, this compound is involved in the reaction Hydroxyphenylacetyl-CoA + Glycine ↔ Hydroxyphenylacetylglycine + CoA, catalyzed by acyltransferase enzymes (EC 2.3.1.-). Hydroxyphenylacetylglycine has been identified in human biofluids.