THE EFFECTS OF PHENYLALANINE ANALOGUES ON THE METABOLISM OF PHENYLALANINE IN RATS

Rats expired14CO2slightly faster when DL-phenylalanine-1-14C rather than DL-phenylalanine-3-14C was injected. An injection of DL-fluorophenylalanine-3-14C produced more radioactive CO2than did phenylalanine-3-14C; DL-beta-thienylalanine-3-14C produced only trace amounts of14CO2but significant levels of radioactivity in the urine. When an excess of one of the nonradioactive phenylalanine analogues was injected at the same time as radioactive phenylalanine, the catabolism of the radioactive amino acid was accelerated. This was shown by an increase in the radioactivity in both the CO2and urine when beta-thienylalanine or 2-amino-3-phenylbutanoic acid was used, and in the urine alone when fluorophenylalanine was used. The incorporation of radioactive phenylalanine into tissue proteins was decreased when one of the nonradioactive phenylalanine analogues was injected simultaneously. However3the incorporation into proteins of tyrosine-14C derived from injected phenylalanine-14C was increased under these conditions.