Guanine-specific binding by bleomycin-nickel(III) complex and its reactivity for guanine-quartet telomeric DNA

Bleomycin-Ni(III) [BLM-Ni(III)] complex, generated from oxidation of the corresponding BLM-Ni(II) complex with Ir(IV) or oxone, binds to single-stranded DNA and causes strand scission at specific guanine sites. In the telomeric-like oligodeoxynucleotide d(T2G4)4, the cleavage by the BLM-Ni(III) complex occurs preferentially at positions G-9 and G-15 in loop regions. By contrast, this Ni(III) complex does not induce cleavage of G-quartet d(G4T4G4)2, which contains no loop guanines, ESR evidence supports that binding of the N-7 position of guanine occurs axially to the Ni(III) center in BLM. The present results provide interesting insights into Ni-BLM chemistry.