gamma-Glutamylphenylalanine is a dipeptide composed of gamma-glutamate and phenylalanine, and is a proteolytic breakdown product of larger proteins. It is probably formed by transpeptidation between glutathione and the corresponding amino acid, catalyzed by gamma-glutamyl transpeptidase. gamma-Glutamylphenylalanine belongs to the family of N-acyl-alpha amino acids and derivatives. These are compounds containing an alpha amino acid which bears an acyl group at its terminal nitrogen atom. gamma-Glutamylphenylalanine is an incomplete breakdown product of protein digestion or protein catabolism. Some dipeptides are known to have physiological or cell-signaling effects although most are simply short-lived intermediates on their way to specific amino acid degradation pathways following further proteolysis. It can be detected in the urine of patients with phenylketonuria, which is a human genetic disorder due to the lack of phenylalanine hydroxylase to metabolize phenylalanine to tyrosine. gamma-Glutamylphenylalanine is found in adzuki bean, onion (Allium cepa), garlic (Allium sativum), and soybean.