POLYRIBOSOME DISAGGREGATION AND CELL-FREE PROTEIN SYNTHESIS IN PREPARATIONS FROM CEREBRAL CORTEX OF HYPERPHENYLALANINEMIC RATS1

Authors

  • F. L. Siegel,

    1. Departments of Pediatrics and Physiological Chemistry and the Joseph P. Kennedy, Jr. Laboratory, University of Wisconsin Medical Center, Madison, Wisconsin
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  • K. Aoki,

    1. Departments of Pediatrics and Physiological Chemistry and the Joseph P. Kennedy, Jr. Laboratory, University of Wisconsin Medical Center, Madison, Wisconsin
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    • 2

      Department of Pediatrics, Jikei University School of Medicine, Tokyo, Japan.

  • R. E. Colwell

    1. Departments of Pediatrics and Physiological Chemistry and the Joseph P. Kennedy, Jr. Laboratory, University of Wisconsin Medical Center, Madison, Wisconsin
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  • 1

    This study was supported by U.S. Public Health Service Grants HD 00341 and HD 00131.

Abstract

Abstract— Seven-day-old rats were injected intraperitoneally with l-phenylalanine (1 g/kg) and the time course of brain polyribosome disaggregation and changes in brain levels of phenylalanine, tryptophan and tyrosine were determined. Disaggregation of brain polyribosomes preceded the increase in levels of phenylalanine in brain, and followed the same time course as depletion of tryptophan from brain.

The effects of several metabolites of phenylalanine (which are formed in phenylketonuria) on protein synthesis in vitro was determined for brain and liver systems. None of the compounds tested was inhibitory at concentrations below 10 mM and in all cases hepatic protein synthesis was more sensitive to inhibition than was the corresponding system from brain.

Ribosomal dimers, formed in brain after injection of phenylalanine, were incapable of supporting high levels of protein synthesis in vitro, a finding that suggested that the inhibition of protein synthesis in vitro in cell-free systems of brain tissue after injection of phenylalanine into young rats was mediated by disaggregation of brain polyribosomes associated with tryptophan deficiency in brain.

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