Critical electrolyte concentration and dispersion of birefringence in heterochromatin and euchromatin of copper sulfate-treated specimens of Triatoma infestans Klug.

Binding of toluidine blue molecules to DNA phosphates under Mg2+ competitive staining conditions and dispersion of birefringence were studied in heterochromatin and euchromatin of Malpighian tubule cells of the hemipteran, Triatoma infestans; 24 h after treatment with copper sulfate. The objective was to detect whether copper binds to chromatin DNA, affecting the critical electrolyte concentration (CEC) value and the chromatin anisotropy in these chromatin types. A decrease in CEC values as measured by metachromasy abolition, and in the concentration of Mg2+ leading to a change from anomalous dispersion of birefringence to normal dispersion of birefringence was found for the heterochromatin and euchromatin of two different nuclear types in the copper-treated material. Protein dissociation from DNA, leading to increased numbers of DNA phosphates available for dye binding, promoted by Mg2+ concentrations above that corresponding to the CEC point is suggested. Based on anisotropy findings, the binding of copper to DNA was assumed not to affect the usual molecular orientation of the DNA.