Fluorescence detection of aromatic amino acid side-chains

Fluorescence detection of aromatic amino acid side-chains 

It is the aromatic amino acid side-chains that give proteins their fluorescent characteristics. If these aromatic groups are damaged, the fluorescence is modified. However, phenylalanine fluorescence is not observed in the presence of other aromatic groups and tyrosine fluorescence is detected only in the absence of tryptophan (Teale, 1960). Even in proteins containing high relative proportions of tyrosine to tryptophan, the fluorescence of the former is masked. 

Proteins are assessed for oxidative modification by measuring the following  

the reduction in the emission intensity of the intrinsic fluorescence of tryptophan intrinsic tryptophan fluorescence on excitation in the wavelength range 279-298 nm occurs in the range 320-350 nm, depending on the protein being studied. Shifts in the emission maximum of the intrinsic fluorescence are an indication of the modified environment of the side-chain, reduction in the fluorescence intensity indicates a structural modification. 

the appearance of iV-formylkynurenine, an oxidative breakdown product of tryptophan  

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