Phenylalanine metabolism in control subjects, mental patients, and phenylketonurics.

Abstract

After injection of dl-phenylalanine-1-C14 or l-phenylalanine-1-C14, C14O2 specific activities in whole blood were frac15–frac13 as high as those after injection of dl-tyrosine-1-C14 or l-tyrosine-1-C14 in normal subjects and chronic psychotic patients. In phenylalanine-C14 studies, tyrosine specific activities were 1/16–1/10 of corresponding phenylalanine specific activities. After injection of l-phenylalanine-1-C14 into two phenylketonuric (PKU) patients, C14O2 activities in one, a child, approximated those in other experiments, whereas they were lower in the adult PKU-patient. Maximal tyrosine specific activity (adult PKU patient) was frac16 the corresponding phenylalanine specific activity. Ratios of specific activities of maximal C14O2 to phenylalanine were similar in the control subject and PKU patient, suggesting that catabolism of phenylalanine proceeds at the same rate in phenylketonuria. Results with l-phenylalanine-U-C14 indicated that more than the carboxyl carbon contributed to blood 14O2. The data suggest that hydroxylation of phenylalanine to form tyrosine may be a minor pathway in intermediary metabolism of phenylalanine in normal humans and in chronic psychotic and phenylketonuric patients. Submitted on April 11, 1962