The Influence Of Ionic Strength On The Binding Of A Water Soluble Porphyrin To Nucleic Acids

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Nucleic Acids Research


The ionic strength dependences of the binding of tetrakis (4-N-methypyridyl)porphine (H₂TMpyP) to poly(dG-dC) and calf thymus DNA have been determined. For the former system the results are typical of other Intercalators, i.e., a plot of log K vs log [Na⁺] is linear albeit with a slope which suggests that the “effective charge” of the porphyrin is closer to two than the formal charge of +4. For calf thymus DNA, the binding profile is not completely compatible with the predictions of condensation theory. Whereas the avidity of binding does decrease with increasing [Na⁺] as predicted, of greater interest is the relocation of the porphyrin from GC-rich regions to AT-rich regions as the ionic strength increases.