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Spectroscopic and thermodynamic study of the interaction of cobalt(III) ammine cations and DNA
Abstract
The binding environments of $\rm Co(NH\sb3)\sb6\sp{3+}$ on polymeric DNA were investigated by $\sp{59}$Co NMR experiments. The fraction of strong binding sites on the polymeric DNAs is highly correlated with the percentages of GC base pairs and GG dinucleotides. Base sequence effects on the interaction of $\rm Co(NH\sb3)\sb6\sp{3+}$ and DNA were further clarified by studying oligomeric DNAs of defined sequence. Based on the mobility of $\rm Co(NH\sb3)\sb6\sp{3+},$ the oligodeoxynucleotides studied can be categorized in three groups. The first group of oligomeric DNAs strongly inhibit the mobility of cobalt(III) ammine cations, and they contain a stretch of contiguous guanine residues or d(*CG*CG*CG*CG) (*C = 5-methylated cytosine). The second group of DNA oligomers have little effect on the cation mobility, and their base sequences are rich in adenines or thymidines. The perturbation of the cation mobility exerted by the third group of oligomeric DNAs falls between the above two extremes; this includes d(CTCTAGAG) and d(GCGCGCGC). The interactions of the two enantiomers of tris(ethylenediammine)cobalt(III) with the oligomeric DNAs were also explored. DNAs from the last two groups show no discrimination in binding toward these two enantiomers. However, DNAs from the first group do show such discrimination. These DNAs bind preferentially to the enantiomer with complementary chirality. The interaction between cobalt(III) cations and DNA of the first group strongly affects DNA conformation. The conformational changes include the well known B-Z transition and the B-A transition. The A conformation of d(CCCCGGGG) in a dilute aqueous solution was confirmed by circular dichroism and two dimensional proton NMR. The interaction of cobalt(III) ammine cations and DNAs from the last groups does not significantly perturb DNA conformation. The binding constants of hexaamminecobalt(III) cation to oligodeoxynucleotides were obtained by equilibrium dialysis. Though the salt dependence of the binding constant for oligomeric DNA is similar to that for polymeric DNA, the absolute magnitude of the binding constant is smaller for oligomeric than for polymeric DNA.
Subject Area
Biophysics
Recommended Citation
Xu, Qiuwei, "Spectroscopic and thermodynamic study of the interaction of cobalt(III) ammine cations and DNA" (1992). ETD collection for University of Nebraska-Lincoln. AAI9314446.
https://digitalcommons.unl.edu/dissertations/AAI9314446