Sulfhydryls with 2-Bromoethylamine

Dissolve the protein or peptide to be aminoalkylated at cysteine sulfhydryls in 0.5 M sodium carbonate. If cystine disulfides are present, add a 10- to 25-fold molar excess of DTT to fully reduce them to free sulfhydryls. 

Add a quantity of 2-bromoethylamine to obtain a 10-fold molar excess over the number of sulfhydryls present in the sample, including any added DTT. 

2-Bromoethylamine may undergo two reaction pathways in its modification of sulfhydryl groups in proteins (Fig. 84). In the first scheme, the thiolate anion of cysteine attacks the No. 2 carbon of 2-bromoethylamine to release the halogen and form a thioether bond (Lindley, 1956). This straightforward reaction mechanism is similar to the modification of sulfhydryls with iodoacetate (Section 4.2). In a two-step, secondary 

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