Of flux and flooding: the advantages and problems of different isotopic methods for quantifying protein turnover in vivo : II. Methods based on the incorporation of a tracer

Curr Opin Clin Nutr Metab Care. 2001 Jan;4(1):51-6. doi: 10.1097/00075197-200101000-00010.


The most common methods for measuring the incorporation of tracer amino acids into tissue protein are the constant tracer infusion and the flooding dose. The flooding dose is an attractive method for measuring tissue protein synthesis because of its convenience and precision. A primary assumption of the method, that the free amino acid precursor pools are equilibrated with the true precursor pool, aminoacyl-transfer RNA, has recently been validated. When short labelling periods are involved, the large dose of amino acid does not appear to alter protein synthesis. The constant tracer infusion is a satisfactory method from a theoretical point of view, but its use requires the measurement of the protein synthetic precursor pool. The best estimate of the aminoacyl-tRNA precursor pool for the constant infusion method appears to be the acid-soluble tissue pool in muscle and VLDL apolipoprotein B-100 in the liver. The experimental approach chosen for measuring tissue protein synthesis should be dictated by the question being addressed.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Amino Acids / metabolism
  • Amino Acids / pharmacokinetics*
  • Aminoacyltransferases / metabolism
  • Animals
  • Humans
  • Isotope Labeling / instrumentation
  • Isotope Labeling / methods*
  • Liver / metabolism
  • Muscle Proteins / metabolism*
  • Protein Biosynthesis*
  • RNA, Transfer, Amino Acyl / metabolism*
  • Reproducibility of Results
  • Time Factors


  • Amino Acids
  • Muscle Proteins
  • RNA, Transfer, Amino Acyl
  • Aminoacyltransferases