Reprint of: Fluorescence and the Structure of Proteins. I. Effects of Substituents on the Fluorescence of Indole and Phenol Compounds.

The quantum efficiency of fluorescence was measured for simple derivatives of indole and phenol and for tryptophyl and tyrosyl residues in peptides and proteins. Fluorescence of these compounds decreased as the electronegativity of substituents increased. In proteins, one strongly electronegative structure is the peptide bond. It is proposed that the observed, low fluorescence of tryptophyl and tyrosyl residues in proteins is attributable in large measure to the presence of this bond.