PHENYLALANINE METABOLISM IN THE PHENYLPYRUVIC CONDITION. II. AN ATTEMPT TO CALCULATE THE DAILY INCORPORATION OF PHENYLALANINE INTO PROTEINS*

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Abstract
From the apparent distribution volume of free phenylalanine, its pool size, and turnover rate in human phenylketonuria which were estimated in the preceding paper, the upper average limit of protein synthesis in 4 phenylketonuric subjects was calculated. When the average phenylalanine content was assumed to be 5%, the limit was 424 g (+121, -71) protein per day per 70 kg body weight. Calculations from the data of San Pietro and Rittenberg gave a lower limit of pro-tein synthesis (about 330 g per day). In one phenylketonuric subject the lower limit of plasma protein synthesis was estimated to be 17 g, per day per 70 kg body weight; this approximated 3% of the total body protein formation. The turnover time of 28.4 days for the plasma proteins was well within the limits given by other investigators. The authors consider protein synthesis in phenylketonuric subjects to be quantitatively similar to that in non-phenylketonuric individuals. The assumptions and the model on which the experiments and the results were based are discussed.