Bleomycin-DNA interactions: fluorescence and proton magnetic resonance studies

Abstract

The interaction of the antitumor agent bleomycin A2 with DNA was examined by fluorescence spectroscopy and PMR techniques. Fluorescence bands observed at 353 and 405 nm in the spectrum of bleomycin were assigned to the bithiazole and 4-aminopyrimidine rings, respectively. Quenching of bithiazole fluorescence by DNA was used to determine apparent equilibrium constants for the complex which, in 2.5 mM tris(hydroxymethyl)aminomethane buffer, pH 8.4, are 1.2 .times. 105 M-1 for bleomycin and 1.4 .times. 105 M-1 for tripeptide S, a partial acid hydrolysis product of the antibiotic. Under these conditions, 1 molecule of bleomycin binds for every 5-6 base pairs in DNA. In the PMR spectrum of bleomycin, resonances emanating from the bithiazole rings and dimethylsulfonium groups are preferentially broadened and reduced in intensity in the presence of DNA, suggesting that these moieties bind most tightly to the polymer.