Interaction of cis- and trans-dichlorodiammineplatinum(II) with synthetic polydeoxyribonucleotides: Effect on equilibrium buoyant densities

Abstract

Equilibrium buoyant densities in Cs 2SO 4 of four synthetic double-stranded polydeoxyribonucleotides were compared following reaction with either cis-Pt(NH 3) 2Cl 2, trans-Pt(NH 3) 2Cl 2 or PtCl 4. While both Pt(NH 3) 2Cl 2 isomers caused significant increases in the buoyant densities (ϱ) of the two G + C polymers, the cis- isomer increased the ϱ of poly[d(G−C)] and the trans- isomer increased the ϱ of poly(dG) · poly(dC) more sharply than the corresponding isomer at low molar ratios of metal ion to polymer. Chloroplatinic acid was without effect. Only cis-Pt(NH 3) 2Cl 2 produced substantial increases in the ϱ of poly[d(A−T)] and poly(dA) · poly(dT) with increasing metal ion concentrations. These increases were accompanied by a proportional decrease in the thermal transition temperature (T m) of poly(dA)-poly(dT) and a sharp increase in the T m of poly[d(A−T)]. Our results indicate that the cis- isomer reacts with all four polymers to produce ϱ changes clearly distinct from those values observed after reaction with either the trans- isomer or PtCl 4. These results help explain the observation by others that the cis- isomer produces greater ϱ changes in native DNA than the trans- isomer. On the basis of our data and the published results of others, one may rationalize the quantitative differences between the cis- and trans- compounds on the buoyant densities of naturally occurring DNA; however, additional studies are clearly needed.