ABSTRACT
The specific chemical modification of tryptophan in proteins is one of the more challenging problems in protein chemistry. First, solvent conditions for providing specificity of modification are, in general, somewhat harsh. This, however, is not an absolute and it possible to obtain satisfactory results under mild reaction conditions with some proteins. Second, there is considerable possibility of either the concomitant or the separate modification of other amino acid residues. Third, analysis for the determination of the exact extent of modification requires a rigorous approach combining spectral analysis and amino acid analysis
after hydrolysis in a solvent that will not destroy tryptophan. Friedman has written an excellent review
of the measurement of tryptophan by amino acid analysis, with a discussion of the specific reaction of ninhydrin with tryptophan.
