The fluorescence of tyrosyl and tryptophanyl diketopiperazines.

The influence of the peptide group on the quantum yield of phenol and indole has been evaluated from fluorescence measurements on the diketopiperazines of the two chromophores. Strong quenching of both groups occurs in water which is almost completely eliminated in dioxane and dimethyl sulfoxide. Polarization of fluorescence measurements indicate that the diketopiperazines have folded conformations in 95% glycerol solutions. It is suggested that the low yields of tyrosyl and tryptophanyl emission in the native state of proteins may be accounted for, in part, by their interactions with the peptide group.