The reaction of bleomycin with DNA in vitro was shown to occur by a decrease in the melting temperature (Tm of DNA. This decrease of Tm was observed when DNA was incubated with the antibiotic in the presence of a sulfhydryl compound such as 2-mercaptoethanol or dithiothreitol. It was also observed when DNA was incubated with 2-mercaptoethanol, dialyzed and thereafter bleomycin A2 was added. It was not observed when DNA was incubated with bleomiycn A2 alone and with the addition of 2-mercaptoethanol just before the determination of Tm. The results indicate that, although 2-mercaptoethanol has no effect on Tm, DNA must react with 2-mercaptoethanol since the Tm of DNA after the reaction is decreased, as shown by the reaction with bleomycin A2. The effect of bleomycin A2 on DNA in the presence of the sulfhydryl compound was diminished by the addition of Cu2+, Zn2+ or Co2+. Bleomycin mixture or bleomycin A2 in the copper-containing form does not significantly affect Tm. Bleomycins and phleomycins are closely related peptide antibiotics, but phleomycin increased the Tm of DNA irrespective of the presence of the sulfhydryl compound. © 1969.
