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A6. Reactions of Cysteine

  • Page ID
    4693
  • [ "article:topic", "authorname:jjakubowskih", "license:ccbyncsa" ]

    Cysteine is a potent nucleophile, which is often linked to another Cys to form a covalent disulfide bond.

     

    Figure:  CYSTEINE REACTIONS 1

    • reacts with iodoacetic acid in an SN2 rx., adding a carboxymethyl group to the S.
    • reacts with iodoacetamide in an SN2 rx, adding a carboxyamidomethyl group to S.
    • reacts with N-ethylmaleimide in an addition rx. to the double bond


     

    Figure:  a quick review of sulfur redox chemistry

     


     

    Figure: CYSTEINE REACTIONS 2

    • reacts with R'-S-S-R'', a disulfide, in a disulfide interchange reaction, to form R-S-S-R'
    • reacts with oxidizing agents like HCOOOH, performic acid, to form cysteic acid.
    • reacts with 5,5-Dithiobis (2-nitrobenzoic acid) (DTNB or Ellman's reagent) in a RSH displacement reaction in which DTNB is cleaved and the 2-nitro-5-thiobenzoic acid anion, which absorbs at 412 nm, is released. Used to quantitate total RSH in a protein