Chromatographic analysis of the adducts formed in DNA complexed with cis-diamminedichloroplatinum(II)

DNA (calf thymus) was reacted to completion with varying amounts of (195mPt)-cis-diamminedichloroplatinum(II) and then hydrolyzed in formic acid at 110 degrees C for 15 min. The hydrolysate was then applied to an Aminex A6 cation-exchange column and eluted with potassium carbonate (0.01 M, pH 11). For a molar ratio of bound Pt per nucleotide (r) of 0.06 or less, most of the radioactivity eluted in the form of two products identified as (1) a bifunctional homoadduct formed between Pt and two guanine residues, and (2) a bifunctional heteroadduct formed between Pt and a residue each of adenine and guanine. The amount of heteroadduct was about 20% of that of the homoadduct. When r was greater than r = 0.06, several additional peaks were observed, one of which was tentatively identified as a monofunctional adduct of guanine and Pt. For all r values, a portion of the Pt, amounting to approximately 20%, eluted in the void volume and may reflect a partial breakdown of the adducts during hydrolysis.