ABSTRACT
The specific chemical modification of tryptophan in protein is one of the more challenging problems in protein chemistry. Treatment of tryptophan with hydrogen peroxide results in the oxidation of the indole ring. The conversion of tryptophanyl residues to 1-formyltryptophanyl residues has been reported. The reaction conditions are somewhat harsh, but the procedure is reversible and should prove quite useful for small peptides and has been applied to at least two proteins. One of the most useful modification procedures for tryptophanyl residues in proteins involves the use of 2-hydroxy-5-nitrobenzyl bromide and its various derivatives. 2-Hydroxy-5-nitrobenzyl bromide, frequently referred to as Koshland's reagent, was introduced by Koshland and co-workers. A heterobifunctional reagent based on the o-nitrophenylsulfenyl compounds has been recently developed by Demoliou and Epand. An example of a particularly good study on the modification of tryptophan in proteins and peptides is that of Hazum and co-workers on luteinizing–hormone–releasing hormone.
