Aminoacyl-tRNA enrichment after a flood of labeled phenylalanine: Insulin effect on muscle protein synthesis

Giuseppe Caso, G. Charles Ford, K. Sreekumaran Nair, Peter J. Garlick, Margaret A. McNurlan

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


Muscle protein synthesis in dogs measured by flooding with L-[2H5] phenylalanine (70 mg/kg) was significantly stimulated by infusion of insulin with amino acids. The stimulation of muscle protein synthesis was similar when calculated from the enrichment of phenylalanyl-tRNA (61 ± 10%, P < 0.001), plasma phenylalanine (61 ± 10%, P < 0.001), or tissue fluid phenylalanine (54 ± 10%, P < 0.001). The time course for changes in enrichment of L-[2H5]phenylalanine throughout the flooding period was determined for plasma, tissue fluid, and phenylalanyl-tRNA in the basal state and during the infusion of insulin with amino acids. Enrichments of plasma free phenylalanine and phenylalanyl-tRNA were equalized between 20 and 45 min, although the enrichment of phenylalanyl-tRNA was lower at early time points. Rates of muscle protein synthesis obtained with the flooding method and calculated from plasma phenylalanine enrichment were comparable to those calculated from phenylalanyl-tRNA and also to those obtained previously with a continuous infusion of phenylalanine with phenylalanyl-tRNA as precursor. This study confirms that, with a bolus injection of labeled phenylalanine, the enrichment of aminoacyl-tRNA, the true precursor pool for protein synthesis, can be assessed from more readily sampled plasma phenylalanine.

Original languageEnglish (US)
Pages (from-to)E1029-E1038
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number5 45-5
StatePublished - 2002


  • Amino acids
  • Dog
  • Flooding technique
  • Ketoisocaproic acid
  • L-[H]phenylalanine
  • Stable isotopes

ASJC Scopus subject areas

  • General Medicine


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