Effect of Dietary Conditions on Metabolism of Phenylalanine, Tyrosine and Isoleucine in the Growing Chick

Abstract

Oxidative degradation of phenylalanine, tyrosine and isoleucine was measured in chicks fed a control, phenylalanine-, isoleucine- and amino acid-free diets and fasted.
Oxiditative degradation of phenylalanine was markedly decreased for a phenylalanine- and amino acid-free diets as compared with controls, whereas that of tyrosine was apparently unaffected for a phenylalanine-free diet and decreased a little for an amino acid-free diet. With regard to isoleucine, less oxidative degradation per chick was observed for an isoleucine- and amino acid-free diets than that for a control diet.
The decrease in phenylalanine degradation was due, at least in part, to a block before the formation of tyrosine in the catabolic pathway. This phenomenon was accompanied by increased incorporation in phenylalanine-¹⁴C into body. The results suggest the existence of adaptive mechanisms that function to conserve phenylalanine specially.
But the excretion of radioactivity to excreta increased by phenylalanine-depleted animals and the most of radioactivity was found in the phenylalanine fraction when phenylalanine-¹⁴C was injected.