Protein standard absolute quantification (PSAQ) method for the measurement of cellular ubiquitin pools

Nat Methods. 2011 Jul 10;8(8):691-6. doi: 10.1038/nmeth.1649.


The protein ubiquitin is an important post-translational modifier that regulates a wide variety of biological processes. In cells, ubiquitin is apportioned among distinct pools, which include a variety of free and conjugated species. Although maintenance of a dynamic and complex equilibrium among ubiquitin pools is crucial for cell survival, the tools necessary to quantify each cellular ubiquitin pool have been limited. We have developed a quantitative mass spectrometry approach to measure cellular concentrations of ubiquitin species using isotope-labeled protein standards and applied it to characterize ubiquitin pools in cells and tissues. Our method is convenient, adaptable and should be a valuable tool to facilitate our understanding of this important signaling molecule.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Humans
  • Isotope Labeling / methods*
  • Mass Spectrometry / methods*
  • Mass Spectrometry / standards*
  • Subcellular Fractions / metabolism*
  • Ubiquitin / metabolism*
  • United States


  • Ubiquitin