Hyperthermic Modification of Bleomycin-DNA Interaction Detected by Electron Spin Resonance

Electron spin resonance spectra of DNA labeled with each of four spin-labeling compounds have been studied to detect interaction between the antibiotic bleomycin and DNA. Only one of these labels, compound IV, resulted in a modified spectrum when bound to DNA and the latter was subjected to bleomycin. This property has been used to monitor DNA-bleomycin interactions under physiological and hyperthermic conditions. Bleomycin produced an increase in rotational correlation time of the residue bound to DNA at 37°C and a significantly higher increase at 43°C. Some effect was still detected with bleomycin at 37°C after preheating at 43°C. Parallel studies have revealed enhanced binding of ${}^{59}{\rm Fe}\text{-bleomycin}$ to DNA during and after hyperthermic treatment.