On the determination of the time required for biosynthesis of a single protein molecule: experiments with rat pancreatic ribonuclease

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Abstract
Activity-time curves were determined for the incorporation of radioactive aliphatic amino acids into the ribonuclease of rat-pancreas slices. In contrast with results obtained by other workers in vivo, no appreciable delay was observed before the appearance of radioactivity in protein. The results are discussed in relation to various time factors in the biosynthesis of protein. It is suggested that exchange may be a limiting form of a template mechanism of protein synthesis, and that while exchange may play only a small part in normal protein synthesis in vivo, it may become a dominant route for amino acid incorporation in vitro when cellular organization is disrupted or modified. The radioactivity in crude enzymic hydrolysates of yeast or Chlorella protein is much more rapidly incorporated into ribonuclease than is the activity of purified hydrolysates. The activating factor was not identified.