Modification of Tryptophan with 2-Hydroxy-5-Nitrobenzylbromide

  • Dan S. Tawfik
Part of the Springer Protocols Handbooks book series (SPH)


2-Hydroxy-5-nitrobenzylbromide, Koshland’s reagent (1), reacts rapidly and under mild conditions with tryptophan residues. At low pH (<7.5), this reagent exhibits a marked selectivity for tryptophan; under more basic pH or at higher reagent concentrations, cysteine, tyrosine, and even lysine residues can be modified as well. The reaction is extremely rapid either with the protein or with water. The reagent is relatively insoluble in water; it is therefore necessary first to dissolve it in an organic solvent (e.g., dioxane) and then to add it to the protein solution in buffer. Unlike most other modifying reagents, the final organic solvent concentration in the reaction mixture is relatively high (5–15%). Determination of the number of modified tryptophans is achieved spectrophotometrically.


Sodium Hydroxide Lysine Residue Marked Selectivity Protein Solution Tryptophan Residue 
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  1. 1.
    Horton, H. R. and Koshland, D. E., Jr. (1972) Modification of proteins with active benzyl halides. Methods Enzymol. 25, 468–482.CrossRefGoogle Scholar

Copyright information

© Humana Press Inc., Totowa, NJ 1996

Authors and Affiliations

  • Dan S. Tawfik
    • 1
  1. 1.Department of Chemical ImmunologyWeizmann Institute of ScienceRehovotIsrael

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