Direct Labelling of Proteins with 125I


To quantify binding to receptors and endocytosis of protein ligands, radioactive labelling with 125I is still the most widely used technique. It combines high sensitivity with simple analysis and is the method of choice for most applications. Radioactive iodine can be directly coupled to tyrosine residues or via adducts that accumulate in the cells at their site of degradation. Two different methods for rapid direct labelling of proteins can be used for studying in vivo metabolism (blood clearance and degradation) or receptor kinetics and cellular uptake and degradation.

Key Concepts

  • Tracing labelled proteins in vitro and in vitro.
  • Protein binding to receptors.
  • Endocytosis and subcellular trafficking of proteins.
  • Lysosomal degradation.
  • Radioactive tracers.

Keywords: endocytosis; protein labelling; receptor; ligand; iodination; protein degradation


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Further Reading

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Zupan AA and Johnson EM Jr (1991) Evidence for endocytosis‐dependent proteolysis in the generation of soluble truncated nerve growth factor receptors by A875 human melanoma cells. Journal of Biological Chemistry 266 (23): 15384–15390. PubMed PMID: 1651328.

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How to Cite close
Gjøen, Tor, and Berg, Trond(Nov 2016) Direct Labelling of Proteins with 125I. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0003771.pub2]