A Colorimetric Procedure for the Quantitative Determination of Tryptophan Residues in Proteins

Abstract

A simple method for the determination of tryptophan residues in proteins is described. The method involves (a) treatment of the protein with an excess of 2-hydroxy-5-nitrobenzyl bromide, (b) purification of the labeled protein by gel filtration and ethanol washing, (c) measurement of the absorbance at 410 mµ to determine the number of colored groups incorporated, and (d) a determination of the total protein content by conventional methods. The procedure has been shown to be accurate with a wide variety of proteins.