1976 年 96 巻 7 号 p. 891-898
Studies were made on the intermolecular interaction of the oxazine dye Nile Blue A and calf-thymus deoxyribonucleic acid (DNA). It was concluded from these experimental results that two modes of interaction, ionic binding of the basic dye and the phosphate group of DNA, which leads to metachromasis of the dye, and intercalation of the dye between adjacent base-pairs of the macromolecule, are taking part in the binding of Nile Blue A and DNA : (1) When this dye was mixed with DNA at pH 7.0, intensity of its characteristic absorption bands (α and β bands) decreased, and new absorption bands appeared in the vicinity of 550 nm (γ band) and 668 nm (δ band). (2) The γ-band was produced when the molar ratio of [Dye]/[DNA-P] was greater than 1, while the δ-band was produced when this molar ratio was smaller than 1. (3) Flow dichroism spectrum of the δ-band indicated that the Nile Blue A molecule was oriented perpendicularly to the longer axis of the double helix of DNA ; dichroism was not observed with a mixture of this dye and heat-denatured DNA. (4) The γ absorption band was also produced by the mixed system of Nile Blue A and potassium poly (vinylsulfonate) : no spectral change was observed with a monomeric vinyl sulfonate. (5) Mixed systems of Nile Blue A and a high concentration of purine nucleosides or mononucleotides exhibited a larger δ band than the systems in which corresponding pyrimidine derivatives were involved. (6) Larger spectral changes were produced by the interaction systems of Nile Blue A and purine homopolynucleotides than by the systems in which pyrimidine homopolynucleotides were involved. (7) Viscosity and melting temperature of DNA increased with increasing concentration of this dye added.