Interaction of bleomycin A2 with poly(deoxyadenylylthymidylic acid). A proton nuclear magnetic resonance study of the influence of temperature, pH, and ionic strength

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Abstract
The binding of bleomycin A2 to poly(deoxyadenylylthymidylic acid) [poly(dA-dT)] was monitored by proton NMR spectroscopy. An analysis of the effects of temperature, ionic strength and pH is included. Sites of drug-nucleic acid interaction were delineated on the basis of chemical shift perturbations of drug and nucleic acid resonances. The binding of the antibiotic occurs with partial intercalation of the aromatic bithiazole group and immobilization of the cationic dimethylsulfonium group. This complex dissociates as the nucleic acid is denatured to the single-stranded form. The absence of significant pH effects suggests that the N terminus of bleomycin A2, which contains the titratable groups, does not contribute to the interaction of the drug molecule with poly(dA-dT). The problems associated with assigning a specific geometry to the drug-nucleic acid complex are discussed. [The bleomycins are used clinically in the treatment of various neoplastic diseases.].

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