Phenylalanine metabolism in control subjects, mental patients, and phenylketonurics

¹ Research Facility, Rockland State Hospital, Orangeburg, New York

After injection of dl-phenylalanine-1-C¹⁴ or l-phenylalanine-1-C¹⁴, C¹⁴O₂ specific activities in whole blood were – 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 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 C¹⁴O₂. 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.