FE-BLEOMYCIN AND CO-BLEOMYCIN BOUND TO SITE-SPECIFIC AND NONSPECIFIC DNA DECAMERS - COMPARATIVE BINDING AND REACTIVITY OF THEIR METAL CENTERS

Co- and Fe-bleomycins (Blms) have been reacted with DNA(a), d(GGAAGCTT CC)(2), containing a specific site for cleavage, and DNA(b), d(GGAAATT TCC)(2), a closely related nonspecific 10-mer, to survey whether featu res of structure and reactivity of these adducts vary systematically a s a function of the base sequence of the DNA oligomer. The ESR spectru m of NO-Fe(II)BlmDNA(a) is rhombically perturbed in comparison with th at of NO-Fe(II)BlmDNA(b), which is nearly identical to the spectrum of NO-Fe(II)BLm. The ESR spectrum of Fe(III)BlmDNA, in phosphate buffer is low-spin; that of Fe(III)BlmDNA(b) is high-spin as seen with Fe(III )Blm alone. According to absorbance spectroscopy, O-2-Fe(II)BlmDNA(a) is stabilized in comparison with the DNA(b) adduct. Similar stabilizat ion of O-2-Co(II)Blm bound to DNA(a) but not to DNA(b) was also observ ed by ESR spectroscopy. HO2-Co(III)Blm A(2) binds in slow exchange on the NMR time scale to DNA(a) at its 5'-G-pyrimidine-3' site of cleavag e. In contrast, fluorescence and NMR spectroscopy demonstrate that mos t of HO2-Co(III)Blm A(2) binds stoichiometrically in fast exchange to DNA(b). The reactions of Fe(m)BlmDNA, and Fe(III)BlmDNA(b) with ascorb ate and O-2 reveal that the latter becomes activated and cleaves its 1 0-mer, producing base propenals; at a faster initial rate. Thus, in tw o series of metallobleomycins, (A) NO-Fe(II)Blm, O-2-Fe(II)Blm, Fe(II) Blm in phosphate buffer, and HO2-Fe(III)Blm and (B) O-2-Co(II)Blm and HO2-Co(III)Blm, the metal domain of each species interacts differently with DNA depending upon its base sequence.