Abstract
The growth retardation and external pathological lesions that occur in rats fed a 10% casein diet containing 5% tyrosine could be alleviated by the supplementation of extra protein (20% casein) or 0.66% methionine plus 0.90% threonine (equivalent to the contents in a 20% casein, . respectively). Liver tyrosine aminotransferase activity is elevated by ingestion of excess tyrosine, but lowered by the supplementa tion of extra casein or methionine plus threonine. In rats fed a high tyrosine diet supplemented with methionine plus threonine, liver p-hydroxyphenylpyruvate hydroxylase activity was not higher than that of the 10% casein group, but liver homogentisate oxidase activity in creased significantly. When excess tyrosine was included in the 10 casein diet, free tyrosine concentrations in plasma, liver, muscle and brain were extremely elevated, but when the high tyrosine diet was sup plemented with extra casein or methionine: plus threonine, theirr plasma and tissues tyrosine concentrations lowered significantly. A large in, crease in total phenols, p-hydroxyphenylpyruvate and free tyrosine excretions in urine was produced in animals fed the high tyrosine-low protein diet, but these were lowered by the supplementation of methio nine and threonine to the diet.
