Carboxymethylation of Cysteine Using Iodoacetamide/Iodoacetic Acid

If cysteine or cystine are identified in a protein, they require modification if they are to be quantified. Thiol groups may be blocked by a variety of reagents, including iodoacetic acid and iodoacetamide. Iodoacetate produces the S -carboxymethyl derivative of cysteine, effectively introducing new negative charges into the protein. Where such a charge difference is undesirable, iodoacetamide may be used to produce S -carboxyamidomethylcysteine (on acid hydrolysis, as for amino acid analysis, this yields S -carboxymethylcysteine). The charge difference between these two derivatives has been utilized in a method to quantify the number of cysteine residues in a protein ([ 1 ], see Chapter 83). These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.