THE INHIBITION OF PROTEIN SYNTHESIS IN A RAT BRAIN SYSTEM BY ETHIONINE IN VITRO AND IN VIVO1

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Abstract
Abstract— An amino acid incorporating system from rat brain has been used to study in vitro four aspects of protein synthesis: amino acid‐AMP‐enzyme complex formation; amino acid‐tRNA synthesis; amino acid incorporation into protein and protein synthesis from presynthesized amino acid‐tRNA. Ethionine (0.5 mm) inhibited the system and the inhibition appeared to be in the formation of amino acid‐tRNA. The inhibition in vitro was independent of the sex of the animal from which the system was derived. Pretreatment of animals in vivo with ethionine yielded in females only preparations deficient in incorporating capacity when tested in vitro. Exchange experiments demonstrated that the defect was in the pH 5 enzymes and not in the ribosomes. The inhibition in vitro was not reversed by addition of ATP and appeared to be competitive with the amino acid substrate.