[Structural changes in cell nuclei in the physiologic pH range]

Fluorescence of the suspension of cell nuclei from rat liver was investigated under neutral pH range. The pH decrease from 7 to 5 causes the quenching of protein fluorescence of nuclei and leads to an increase of the polarization degree of the fluorescence. Buffering properties of the nuclei in this range were detected. The use of 1-anilino-8-naphthalenesulfonate as the fluorescent probe permits to find the changes of nuclei surface properties with increasing the proton concentration in the solution. Circular dichroism spectra of nuclei were shown to depend on the pH solution too. It was suggested that structure state of the nuclei depends on the pH solution. The structural changes are reversible in the physiological pH range and were concluded to be in the envelope and chromatin of the nuclei. The role of histidine residues of nuclear proteins in the initiation of the structure changes was discussed. It was supposed that structure changes of the nuclei in the physiological pH range have an essential functional role.