Kinetic investigation of the DNA platination reaction: evidence for a transient adduct between deoxyribonucleic acid and cis-platinum(II).

Kinetics of the synthesis of adducts between salmon testis DNA and platinum(II) compounds were measured by their effects on DNA synthesis, circular dichroism, and ethidium bromide dependent fluorescence. Transient incorporation of [14C]cyanide into DNA adducts of of cis-diammineaquochloroplatinum(II) and respectively cis-diamminediaquoplatinum(II) compounds but not of trans-diammineaquochlorplatinum(II) was observed. A minimal kinetic scheme is derived, in which a transient monodentate DNA-platinum(II) adduct is formed in a bimolecular reaction between DNA and aquated platinum(II) compounds. Second-order rate constants are 2000-3000 M-1 min-1 for cis-diamminediaquoplatinum(II) and 280-400 M-1 min-1 for cis- and trans-diammineaquochloroplatinum(II), respectively. The dependence of pseudo-first-order rate constants is not linear for high concentrations of DNA, suggesting competitive formation of more than one primary adduct. The monodentate adducts inhibit DNA polymerase catalyzed DNA synthesis. The biomolecular reaction is followed by a rearrangement (rate constant 0.22 min-1) that gives rise to most of the decrease in the fluorescence intensity and that depends on the state of aquation of the DNA-bound platinum(II) complex. By exchange of coordinated water with a second nucleotide, the monodentate adduct can form cross-links in a reaction joining the rearrangement. Adducts containing a chloro group liberate it by hydrolysis prior to cross-linking. In the case of the trans-platinum(II) adduct, the hydrolysis is aided by the trans effect of the bound first nucleotide.(ABSTRACT TRUNCATED AT 250 WORDS)