A FLUOROSPECTROPHOTOMETRIC STUDY ON BINDING OF ACRIDINE ORANGE WITH DNA AND ITS BASES

To confirm the nature of the binding of acridine orange (AO) with DNA, a fluorospectrophotometric study was made on the AO-DNA system as well as on the AOmononucleoside and AO-mononucleotide systems. In the (I) region of higher AO/DNA ratios, the fluorescence intensity of AO decreased markedly, while in the (II) region of lower AO/DNA ratios it increased markedly. Similar changes were observed with mononucleosides and mononucleotides, though their effects on fluorescence intensity were weak. There is a good parallel between these fluorospectral changes and the changes in the absorption spectrum already reported. Therefore, it was confirmed that there are two types of mechanism of AO-DNA binding, namely, self-association, in the (I) region and intercalation in the (II) region. Comparison of the effects of the four nucleosides upon the fluorescence intensity indicated that the contribution of an A:T nucleotide pair to the enhancement of fluorescence due to intercalation is more important than that of a G:C nucleotide pair. The reversing effects of urea, KC1, and ethylene diamine on AO-DNA binding indicate that in the (I) region, ionic bonding between AO and the phosphate groups of DNA is predominant, while in the (II) region, hydrophobic bonding between AO and the bases of DNA is predominant. A comparative study was made on a typical metachromatic system of AO and heparin. © 1969.