A Defect in the Metabolism of Tyrosine and Phenylalanine in Premature Infants. Iii. Demonstration of the Irreversible Conversion of Phenylalanine to Tyrosine in the Human Organism

In preceding papers (1, 2), it was shown that premature infants fed vitamin C-free cow's milk mixtures, high in protein (5 grams or more per kgm. per day), exhibit a spontaneous defect in their metabolism of tyrosine and phenylalanine, manifested by the urinary excretion of 1-p-hy- droxyphenyllactic and p-hydroxyphenylpyruvic acids. The defect was accentuated by feeding these subjects either amino acid in pure form. Full-term infants fed similar diets did not show the defect spontaneously but it could be induced in them by the ingestion of a single dose (1.0 gram per kgm.) of either amino acid. It was further shown that the administration of 1- ascorbic acid in adequate dosage abolished the spontaneous and artificially induced defect in both premature and full-term infants.