THERMAL ANALYSIS OF POLYANION METACHROMASY: EFFECT OF TEMPERATURE ON METACHROMATIC SOLUTIONS OF NUCLEIC ACIDS AND ACID MUCOPOLYSACCHARIDES

JOHN W. KELLY ¹, LOUIS CHANG ¹, and FRED ROTHSTEIN ¹

¹ Department of Anatomy, The Mount Sinai School of Medicine, New York, New York, and Departments of Anatomy and Physiology, Tufts University School of Medicine, Boston, Massachusetts

Spectra of toluidine blue with acid mucopolysaccharides and nucleic acids were recorded over the temperature range 10-70°C. Metachromatic ratios were inverse, linear functions of temperature. Intercepts and slopes of the thermal plots distinguished acid mucopolysaccharides from nucleic acids. Acid mucopolysaccharide reactions were thermally reversible. Nucleic acid reactions were not strictly reversible; such behavior was not attributable to thermal denaturation. An explanation for the unusual -peak of ribonucleic acid-toluidine blue metachromasy is offered in terms of terminal phosphate groups of ribonucleic acid. Solution data in which the polyanion-dye ratio was approximately 1, representing typical "metachromasy," were subjected to thermodynamic analysis. These data did not fit a common equation deriving equilibrium constants spectrophotometrically by variation of reactant concentrations. This failure supported the view of metachromasy as a phenomenon primarily involving dye-dye interaction. Another equation based only on temperature variation yielded a value of –4 kcal/mole for the chondroitin sulfate-toluidine blue complex, in good agreement with similar published values obtained both in solutions and stained materials.

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