Phenylalanine-pyruvate aminotransferase activity in chicks subjected to phenylalanine imbalance or phenylalanine toxicity.

Two experiments were done to determine the influence of Phe imbalance and excess on Phe-pyruvate aminotransferase (PAT) activity in the chick. Five replicates of 3 chicks (experiment 1) or 2 chicks (experiment 2) of a commercial brown egg layer strain were fed a semipurified diet for 1 wk and then received experimental diets for 10 d. Three diets were used in experiment 1: the basal diet contained 0.46% Phe; the imbalance diet was similar to the basal diet except that it contained a 10% mixture of indispensable amino acids lacking Phe (IAA - Phe) to create a Phe imbalance; the imbalance corrected diet was similar to the imbalance diet except that it was supplemented with 1.12% Phe to correct the imbalance. A 3 x 2 factorial arrangement of treatments in experiment 2 provided 3 dietary levels (0.46, 1.58, and 2.46%) of Phe and either no supplement or 10% supplement of IAA - Phe. Nonfasted chicks were killed and livers were sampled in experiment 1, and livers, kidneys, brains, and pectoralis major muscles were sampled in experiment 2. In experiment 1, liver PAT activity per gram of liver was 80 and 55% higher (P < 0.01) in chicks fed the imbalance and imbalance corrected diets than in chicks fed the basal diet. In experiment 2, the livers and kidneys, but not brains and muscles, of chicks that received the 10% supplement of IAA - Phe had higher activities of PAT per gram of tissue per minute and per milligram of tissue protein extract per minute than chicks that did not receive IAA - Phe (P < 0.001). No effect of dietary Phe on PAT activity was detected (P > 0.05). Phenylalanine-pyruvate aminotransferase activity appears to be regulated in response to dietary content of indispensable amino acids but not by the dietary level of Phe.