title: Studies of metallobleomycins by electronic spectroscopy, electron spin resonance spectroscopy, and potentiometric titration.
abstract: The 1:1 bleomycin-A2-Cu(II) complex shows an absorption maximum at 595 nm (epsilon 120), circular dichroism extrema at 555 nm (delta epsilon + 1.21) and 665 nm (-0.61), and electron spin resonance (ESR) signal with g = 2.211, g = 2.055, and A = 178 x 10(-4) cm-1. The formation constant (log K = 12.630) and deprotonation constant (PKc = 3.585) of the 1:1 bleomycin-Cu(II) complex were determined by computer analysis of potentiometric data. The results of potentiometric titration also indicate that the stability of bleomycin-metal complexes is in the order Fe(II) less than Co(II) less than Ni(II) less than Cu(II) greater than Zn(II) and that these divalent metal complexes have a similar coordination environment. The bleomycin-Cu(II) complex has substantially a square-pyramidal configuration in which the secondary amine nitrogen, pyrimidine(N-1) ring nitrogen, deprotonated peptide nitrogen of histidine residue, and histidine imidazole(N-1) nitrogen coordinate to Cu(II) as planar ligand donors, and the alpha-amino nitrogen as axial donor. The specific Cu(II)-binding site of bleomycin has been compared with that of human serum albumin.
mesh_terms: D001665:Binding Sites; D001761:Bleomycin; D002614:Chelating Agents; D002942:Circular Dichroism; D003035:Cobalt; D003300:Copper; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron; D008280:Magnetics; D008670:Metals; D009532:Nickel; D011199:Potentiometry; D013057:Spectrum Analysis; D015032:Zinc
chemical_list: D002614:Chelating Agents; D008670:Metals; D001761:Bleomycin; D003035:Cobalt; D003300:Copper; D009532:Nickel; D007501:Iron; D015032:Zinc