Metabolism of Lysine and Tryptophan in Growing Rats at Various Dietary Protein Levels(Food & Nutrition)

概要

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The metabolic fates of the carbon skeletons of L-[U-^<14>C]lysine and L-[methylene-^<14>C]tryptophan were investigated in growing rats fed with diets containing different percentages of protein calories (0, 5, 10, 15, and 30 PC%) at 4100 kcal of metabolizable energy per kg of diet. The incorporation of ^<14>C into the body protein 12hr after the injection of ^<14>C-labeled lysine or tryptophan was extremely high in the 0 to 10 PC% groups (about 80% of the injected dose being recovered), and the value decreased in the higher PC% groups. The expired ^<14>CO_2 production from both labeled amino acids was depressed in the lower PC% groups, and then increased with increasing levels of dietary protein, showing an inverse pattern to that of the ^<14>C incorporation into the body protein. The activities of hepatic lysine-ketoglutarate reductase and tryptophan pyrrolase were increased with increasing dietary protein levels, and the response pattern of these enzyme activities resembled that of the expired ^<14>CO_2 production from these ^<14>C-amino acids. These results indicate that the metabolic responses of lysine and tryptophan to dietary protein levels change at around 10 PC%, where the growth rate reached its approximate maximum.
社団法人日本農芸化学会の論文
1991-02-23