Aromatic amino acid incorporation into proteins in rat brain slices: influences of other amino acids affecting transport.

Incorporation of [3H]tryptophan, [3H]tyrosine and [3H]phenylalanine into proteins has been studied in cerebral coronal slices from adult and 1-day-old rats. Unlabelled amino acids greatly increased (histidine) or decreased (leucine, phenylalanine, tyrosine, tryptophan) intracellular levels of the [3H]amino acids, but only slightly decreased their incorporation rates. Effects on uptake were similar in experiments with adult and newborn rats, but patterns of protein synthesis inhibition seemed to differ. Amino acid uptake and subsequent incorporation into proteins were thus not closely associated. Incorporation in slices from adult rats was much slower than in those from newborn rats, and moreover, one half of it was cycloheximide-insensitive. The difference inhibition patterns by other amino acids may thus be explained by multiple mechanisms in cerebral amino acid incorporation into proteins.