Primary Site of Reaction in the in vitro Complex of Phleomycin in DNA

Abstract

PHLEOMYCIN, the specific inhibitor of replication, binds to DNA in vitro, and adenine–thymine base pairs make an important contribution to the reaction¹. Infrared spectra of the complex thus formed suggest that a carbonyl group in the DNA is involved in the binding; the most likely candidate is the carbonyl group at 2′-thymidine; mineral oil mulls of phleomycin and DNA generate infrared spectra that predict most of the characteristics produced by their reaction product (see footnote to Table 1 for details of experiments). There were, however, significant, if subtle, changes in two regions. Thus a band in the DNA spectrum at 1,230 cm⁻¹ shifted in the complex to 1,220 cm⁻¹, undoubtedly representing small variations in PO₄ stretching frequencies and probably indicating a weak interaction between the copper atoms of phleomycin and the PO₄. (This may underlie the precipitation of DNA by increased concentrations of phleomycin.)