Interactions of iron bleomycin, phosphate or cyanide, and DNA: sequence-dependent conformations and reactions. J Biol Inorg Chem 2001 Jun;6(5-6):618-27
Date
07/27/2001Pubmed ID
11472025DOI
10.1007/s007750100239Scopus ID
2-s2.0-0034840501 (requires institutional sign-in at Scopus site) 6 CitationsAbstract
The hypothesis was investigated that axial ligands bound to Fe(III)-bleomycin [Fe(III)Blm] are destabilized at specific 5'-guanine-pyrimidine-3' binding sites but are stable at nonselective dinucleotides. DNA oligomers and calf-thymus DNA were used in reactions with L-Fe(III)Blm, where phosphate and cyanide served as examples of large and small ligands (L). Both ligands underwent dissociation when L-Fe(III)Blm was bound to d(GGAAGCTTCC)2 (I) but not d(GGAAATTTCCC)2 (II) and at large ratios of calf-thymus DNA to drug. Fe(III)Blm is high spin in 20 mM phosphate buffer, signifying the presence of a phosphate adduct. In the titration of HPO4-Fe(III)Blm with calf-thymus DNA, a large excess of DNA was needed to reach the low-spin state, consistent with an equilibrium competition between phosphate and DNA for Fe(III)Blm. Equilibrium constants for binding Fe(III)Blm and CN-Fe(III)Blm to calf-thymus DNA (6.8x10(5) M(-1) and 5.9x10(4) M(-1), respectively, in HEPES buffer at 25 degrees C and pH 7.4) showed that the CN- ligand also reduced the affinity of DNA for the drug. The kinetics of dissociation of CN- from CN-Fe(III)Blm-DNA were slow and first order in bound drug. The reversible nature of these dissociation reactions was shown using 1H NMR spectroscopy of Fe(III)Blm-I in the absence and presence of large excesses of CN- or phosphate. The results are discussed in terms of a two-state hypothesis for the binding of L-Fe(III)Blm to specific and nonspecific dinucleotides. It is proposed that steric restrictions at specific sites inhibit binding of these ligands.
Author List
Li W, Xia C, Antholine WE, Petering DHMESH terms used to index this publication - Major topics in bold
Base PairingBleomycin
Cyanides
DNA
DNA Adducts
Electron Spin Resonance Spectroscopy
Iron
Kinetics
Molecular Conformation
Nucleic Acid Conformation
Phosphates
Spectrometry, Fluorescence
