Neutral Red Fluorescence of Chromatin: Specificity and Binding Mechanism

Neutral Red, Chromatin Fluorescence, Nucleic Acid Cytochemistry, Intercalative Binding to DNA After treatment with neutral red at low concentrations (10-6, 10-5 m), the chromatin o f chicken erythrocytes shows an intensive red fluorescence, which is reduced or prac­ tically abolished when nuclei become stained by using the dye at concentrations higher than 10~* M. Both the fluores­ cence and staining reactions are dependent on the DNA content of chromatin. Neutral red fluorescence o f nuclei increases considerably after treatment with inorganic cations (Al3+, Ba2+), while previous treatments with meth­ ylene blue reduce the fluorescence intensity. The possi­ bility that chromatin fluorescence depends on the inter­ calative binding of neutral red is suggested.

Observations on the Chromatin Staining by Aluminium-Hematoxylin

The staining reaction of chromatin by aluminium -hematoxylin was investigated. Intense staining, which proved dependent on nucleic acid content, was achieved by using either the preformed lake, mordanting followed by hematoxylin, hematoxylin alone or the lake at high ionic strength. Extraction procedures removed aluminium ions from chromatin but the lake was retained. Chromatin fluorescence induced by ethidium bromide and acridine orange was abolished after staining with the lake. Intercalating-like forces are suggested for aluminium -hematoxylin binding to chromatin.