Mechanisms of heat damage in proteins

ε-(γ-L-Glutamyl)-L-lysine was found to have a growth-promoting activity that was approximately equal to the equivalent quantity of L-lysine for both young rats and chicks receiving a lysine-deficient diet. 2. Small quantities of the compound were found in the plasma of the chicks and rats receiving it at the level of 0.4–0.5% on the diet, but none was detected in the rat urine and only a trace in the separated chick urine. 3. Direct intravenous infusion of glutamyl-lysine into rats resulted in higher plasma concentrations; it is suggested that hydrolysis of the ingested peptides may occur largely in the intestinal wall. 4. The findings are discussed in relation to the earlier hypothesis that the formation of glutamyl-lysine cross-linkages in severely heated protein provides an explanation of their reduced nutritional value.