Nutritional implications of the Maillard reaction: the availability of fructose-phenylalanine to the chick.

Fructose-phenylalanine, the Amadori compound resulting when glucose reacts with phenylalanine, was administered to chicks receiving a phenylalanine-deficient crystalline amino acid diet. The chicks did not respond to oral administration of this molecule which indicated it was nutritionally unavailable as a source of phenylalanine. In vitro protein synthesis studies on liver tissue showed that the rate of incorporation of 14C-phenylalanine into liver solids/mg tissue was significantly lower in chicks fed 0.404%-fructose-phenylalanine than in those not fed this compound. However, when fructose-phenylalanine was added directly to the incubation medium, no reduction of amino acid incorporation occurred. The discrepancy between in vitro and vivo results suggests, therefore, that fructose-phenylalanine is metabolized to another molecule which is causative in reducing liver protein synthesis.