Abstract
The injection of neonatal mice with phenylalanine resulted in a rapid decrease in brain polyribosomes and a concomitant increase in monomeric ribosomes. Animals of 1-16 days of age were equally affected by phenylalanine, although the brain polyribosomes of 60-day-old mice were relatively resistant to the effects of phenylalanine. The population of free polyribosomes appeared to be more sensitive to phenylalanine treatment than bound polyribosomes, which were somewhat more resistant to disruption by high concentrations of the amino acid. The effects of phenylalanine were more pronounced with polyribosomes in the cerebral cortex than with those in the cerebellar tissue. The mechanism of polyribosome disruption was shown to be independent of hydrolysis mediated by ribonuclease. Virtually all of the monomeric ribosomes that resulted from phenylalanine treatment were shown to be inactive with regard to endogenous protein synthesis and were present in the cell cytoplasm as vacant couples. These ribosomes were readily dissociated by treatment with 0.5 M-KCl and subsequent ultracentrifugation. These results are discussed in the light of the possibility that high concentrations of phenylalanine disrupt brain protein synthesis by a molecular mechanism that is associated with initiation events.