INTERACTION OF AQUATED CIS-(NH3)2PTII WITH HOMOPOLYNUCLEOTIDES

The binding of aquated cis-(NH3)2PtII to polyriboadenylic acid, polyribocytidylic acid, and polyriboguanylic acid has been studied at pH 7, 37 °C, and an ionic strength of 0.1. The total number of binding sites per nucleotide in each polynucleotide is one; the magnitude of the intrinsic binding constant increases in the order poly(C) < poly(A) < poly(G). The CPD binding profiles for poly(A) and poly(C) are similar, displaying a noncooperative behavior, while the binding profile for poly(G) is more complex and may be described by a number of alternative binding models. The data arc consistent with the model in which the CPD binds very strongly to the four-stranded poly(G) aggregate up to r values of 0.25, at which point the aggregate is disrupted and the subsequent binding affinity, perhaps to the same or a different site, is greatly reduced. This is the first binding data which supports the four-stranded model for poly(G) in solution. The binding affinity of CPD to homopolynucleotides is greater than to the corresponding nucleosides. The results of these studies are compared and discussed relative to similar investigations reported for other metal ions binding to nucleic acids. © 1979, American Chemical Society. All rights reserved.