Abstract
Free phenylalanine (Phe) and tyrosine (Tyr) in serum, liver and muscle of the rats fed an excess Phe diet were significantly elevated. However, when large amounts of threonine, glutamic acid or histidine were ingested with excess Phe, the elevation of serum Phe and Tyr was considerably prevented. The excess doses of Phe lowered liver phenylalanine hydroxylase (Phe H) activity (Freedland's method) even under the condition of the low Phe pool induced by the excess dose of threonine. Thus, the relationship between serum Phe concentration and liver Phe H activity was not observed definitely in these experiments. By feeding the excess Phe diet most of the amino acids in serum except Phe and Tyr were decreased, whereas each amino acid concentration in liver was not extensively changed. When the rats fed the excess Phe diet were fasted overnight (16hrs.), the Phe and Tyr concentrations in both serum and liver were lowered to 1/6 and 1/30 of those of non-fasting animals, respectively. It was also discussed that the lowered activity of Phe H by the Phe excess dose may be attributed to the relation between the amount of pteridine co-factor and the excess Phe dose.
