Neutral red fluorescence of chromatin: specificity and binding mechanism

After treatment with neutral red at low concentrations (10(-6), 10(-5) M), the chromatin of chicken erythrocytes shows an intensive red fluorescence, which is reduced or practically abolished when nuclei become stained by using the dye at concentrations higher than 10(-4) M. Both the fluorescence and staining reactions are dependent on the DNA content of chromatin. Neutral red fluorescence of nuclei increases considerably after treatment with inorganic cations (Al3+, Ba2+), while previous treatments with methylene blue reduce the fluorescence intensity. The possibility that chromatin fluorescence depends on the intercalative binding of neutral red is suggested.