The basics of thiols and cysteines in redox biology and chemistry

Free Radic Biol Med. 2015 Mar:80:148-57. doi: 10.1016/j.freeradbiomed.2014.11.013. Epub 2014 Nov 27.


Cysteine is one of the least abundant amino acids, yet it is frequently found as a highly conserved residue within functional (regulatory, catalytic, or binding) sites in proteins. It is the unique chemistry of the thiol or thiolate group of cysteine that imparts to functional sites their specialized properties (e.g., nucleophilicity, high-affinity metal binding, and/or ability to form disulfide bonds). Highlighted in this review are some of the basic biophysical and biochemical properties of cysteine groups and the equations that apply to them, particularly with respect to pKa and redox potential. Also summarized are the types of low-molecular-weight thiols present in high concentrations in most cells, as well as the ways in which modifications of cysteinyl residues can impart or regulate molecular functions important to cellular processes, including signal transduction.

Keywords: Cysteine; Free radicals; Redox potential; Redox regulation; Thiols; pK(a).

Publication types

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

MeSH terms

  • Animals
  • Biocatalysis
  • Cysteine / chemistry*
  • Cysteine / metabolism
  • Disulfides / chemistry
  • Disulfides / metabolism
  • Electrons*
  • Free Radicals / chemistry*
  • Free Radicals / metabolism
  • Glutathione / chemistry
  • Glutathione / metabolism
  • Humans
  • Kinetics
  • Oxidation-Reduction
  • Oxidoreductases / chemistry
  • Oxidoreductases / metabolism
  • Signal Transduction*
  • Sulfhydryl Compounds / chemistry*
  • Sulfhydryl Compounds / metabolism
  • Thermodynamics


  • Disulfides
  • Free Radicals
  • Sulfhydryl Compounds
  • Oxidoreductases
  • Glutathione
  • Cysteine