N-Substituted lysines as sources of lysine in nutrition

Twenty seven alpha-N- and epsilon-N-substituted derivatives of lysine belonging to eight different classes: (1) natural dipeptides, (2) alpha-N-acyl-, (3)epsilon-N-acyl-, (4)epsilon-N-(alpha-amino acyl)-, (5)epsilon-N-(omega-amino acyl)-, (6)alpha-N-epsilon-N-di-amino acyl-, (7)epsilon-N-acylglycyl- and (8)Schiff's bases were synthesized. The "in vitro" utilization of some of them was tested by a rat growth assay. Only the derivatives which provided biologically available lysine were hydrolysed by one or more of the intestinal mucosa, liver or kidney homogenates. It is argued that derivatives which can be split by any of the above homogenates are potential sources of lysine. The derivatives of classes (1), (4), (6) and (8) are nearly as efficient as free lysine while lysine in classes (2) and (7) is not utilized at all. From the classes (3) and (5) only some are utilized: epsilon- formyl- and epsilon-acetyl- partially and epsilon-(gamma-glutamyl)-totally. The biologically available derivatives were 4 to 7 times less reactive than free lysine in the Maillard reaction and could therefore be used to fortify foods which have to be submitted to severe heat-treatments. A cheap method of synthesis of epsilon-(gamma-glutamyl)-lysine is proposed and its metabolic transit described.