The uncleaved G–L dipeptide may be absorbed through intestinal brush-border membranes. The G–L dipeptide bond could then be cleaved in the kidney into lysine and 5-oxoproline by γ-glutamylamine cyclotransferase. Because lysine is an essential amino acid for humans and other mammals, the presence of such a pathway might help to satisfy nutritional requirements in the body. 5-Oxoproline, however, should be converted to glutamate by an ATP-dependent enzyme, 5-oxoprolinase, If a large amount of the crosslinked proteins were ingested, the amounts of the G–L dipeptide and subsequently, 5-oxoproline, would increase and thus, a large amount of ATP would be consumed in the kidney. It is feared that such metabolic demands might burden kidney function.