The synergistic effect of Ni(II) and Co(II) on the sulfite induced autoxidation of Cu(II)/tetraglycine was investigated spectrophotometrically at 25.0 degrees C, pH = 9.0, 1 x 10(-5) mol dm(-3) < or = [S(IV)] < or = 8 x 10(-5) mol dm(-3), [Cu(II)]= 1 x 10(-3) mol dm(-3), 1 x 10(-6) mol dm(-3) < or = [Ni(II)] or [Co(II)] < or = 1 x 10(-4) mol dm(-3), [O2] approximately 2.5 x 10(-4) mol dm(-3), and 0.1 mol dm(-3) ionic strength. In the absence of added nickel(II) or cobalt(II), the kinetic traces of Cu(III)G4 formation show a large induction period (about 3 h). The addition of trace amounts of Ni(II) or Co(II) increases the reaction rate significantly and the induction period drastically decreases (less than 0.5 s). The effectiveness of Cu(III)G4 formation becomes much higher. The metal ion in the trivalent oxidation state rapidly oxidizes SO3(2-) to SO3*-, which reacts with oxygen to produce SO5*-. The strongly generated oxidants oxidize Cu(II)G4 to Cu(III).
NiIIGGH (GGH = glycylglycylhistidine) reacts rapidly with S(IV), in air-saturated solution, to produce NiIIIGGH. A mechanism is proposed where initial NiIII oxidizes SO3(2-) to SO3*-, which reacts with dissolved oxygen to produce SO5*-, initiating radical chain reactions. DNA strand breaks and 8-oxo-7,8-dihydro-2'-deoxyguanosine formation were observed in air-saturated solutions containing micromolar concentrations of Ni(II) and S(IV). The extent of DNA damage showed dependence on the ratio of the NiIIGGH : S(IV) concentrations and the ionic strength.
Copper(II)/(III) tetraglycine complexes were investigated for their ability to catalyze the autoxidation of sulfite resulting in oxidative DNA damage. The focus of this work is on DNA damage by Cu(III) and oxysulfur radicals formed by the oxidation of S(IV) oxides by dissolved oxygen in the presence of Cu(II) tetraglycine complexes. The results suggest that sulfite is rapidly oxidized by oxygen in the presence of Cu(II) complexes producing Cu(III) tetraglycine, which can be monitored spectrophotometrically at 365 nm. A synergistic effect of Cu(II) with a second metal ion (Ni(II), Co(II) or Mn(II) traces) was observed.
DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 microM) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O2, DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO3 -, HO and H radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.
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