Reactions Resulting in a Negative Charge

Acylation with dicarboxylic acid anhydrides, e. g. succinic acid anhydride, introduces a carboxyl group into the protein  

Carbamoylation with cyanate attacks a- and 8-amino groups as well as cysteine and tyrosine residues. However, their derivatization is reversible under alkaline conditions  

Arylation with l-fluoro-2,4-dinitrobenzene (Sanger s reagent FDNB) and trinitrobenzene sulfonic acid was outlined in Section 1.2.4.2.2. FDNB also reacts with cysteine, histidine and tyrosine. 

4-Fluoro-3-nitrobenzene sulfonic acid, a reactant which has good solubility in water, is also of interest for derivatization of proteins  

Introduction of a fluorescent acid group is possible by interaction of the protein with pyridoxal phosphate followed by reduction of the intermediary Schiff base  

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