Fluorescence and the structure of proteins. XXI. Fluorescence of aminotyrosyl residues in peptides and helical proteins.

1. Five peptides containing tyrosine were converted to the 3-aminotyrosyl peptides by nitration with tetranitromethane and subseuqent reduction of the nitro groups to amino groups. The fluorescence of these aminotyrosyl residues was found to be quite similar to that of 3-aminotyrosine and it is concluded that the fluorescence is not sensitive to incorporation of the amino acid into the peptide chain. 2. Fluorescence of 3-aminotyrosine derivatives was sensitive, however, to the nature of the solvent; as the dielectric constant decreased, fluorescence was enhanced ten fold and the emission maximum shifted from the 350-370 nm value in aqueous solution to 320 nm. It is predicted that similar differences might be expected for exposed and buried aminotyrosyl residues in a protein. 3. Exposed tyrosyl residues on the helical protein tropomyosin and a helical segment of paramyosin were aminated in part (39% and 34% of the total tyrosyl residues, respectively). The fluorescence of the aminated tyrosyl residues on these proteins was similar to that of the aminotyrosyl peptides in an aqueous medium. Although the fluorescence efficiency of an aminotyrosyl residue was much lower than that of a tyrosyl residue, it was easy to distinguish the fluorescence of the aminotyrosyl residues (350-355 nm) on the protein from that arising from unmodified tyrosyl residues (305 nm).