Copper ion-dependent oxy-radical mediated DNA damage from dihydroxy derivative of etoposide

The dihydroxy etoposide, a metabolite of the clinically active anticancer drug, VP-16, induced extensive DNA damage in the presence of copper ions. While superoxide dismutase was without any effect on the DNA damage, catalase and inhibitors of free hydroxyl radicals inhibited the DNA degradation, indicating that hydroxyl radicals were responsible for this drug-Cu-dependent DNA damage.     

Oxidative stress induced by a copper-thiosemicarbazone complex

Copper thiosemicarbazones cause considerable oxidative stress. This effect may be related to their cytotoxicity. In the present work, the chemical and cellular properties of a new ligand, pyridoxal thiosemicarbazone (H2T), and its copper(II) chelate (CuT) are assessed. CuT is toxic to cultured Ehrlich ascites tumor cells, producing nearly complete cell kill at drug/cell ratios of 2.5-4 nmol/10(5) cells in a monolayer culture over a 48-h treatment period. This concentration is at least 1 order of magnitude lower than those required for a similar degree of cytotoxicity by H2T or CuCl2. The following observations support the view that activated oxygen species are generated by interaction of CuT with Ehrlich cells: (1) Room-temperature electron spin resonance spectroscopy and atomic absorption measurements show rapid cellular uptake and CuT-thiol adduct formation. (2) Cellular thiol content is reduced. (3) High levels of DNA strand scission result from 1-h treatments of cells by concentrations of CuT that cause growth inhibition and toxicity. (4) The extent of strand scission can be increased by addition of superoxide dismutase and decreased by catalase or DMSO in the treatment medium. Catalase and DMSO do not inhibit the toxic effect of CuT. This suggests that DNA damage is not responsible for inhibition of cell proliferation by CuT.     

Vanadium(V) Reduction by Shewanella oneidensis MR-1 Requires Menaquinone and Cytochromes from the Cytoplasmic and Outer Membranes

The metal-reducing bacterium Shewanella oneidensis MR-1 displays remarkable anaerobic respiratory plasticity, which is reflected in the extensive number of electron transport components encoded in its genome. In these studies, several cell components required for the reduction of vanadium(V) were determined. V(V) reduction is mediated by an electron transport chain which includes cytoplasmic membrane components (menaquinone and the tetraheme cytochrome CymA) and the outer membrane (OM) cytochrome OmcB. A partial role for the OM cytochrome OmcA was evident. Electron spin resonance spectroscopy demonstrated that V(V) was reduced to V(IV). V(V) reduction did not support anaerobic growth. This is the first report delineating specific electron transport components that are required for V(V) reduction and of a role for OM cytochromes in the reduction of a soluble metal species.     

How amino acids control the binding of Cu(II) ions to DNA. Part III. A novel interaction of a histidine complex with DNA

L-Histidine Cu(II) complex bound to DNA showed broad EPR signals characteristic of the aggregated Cu(II) species, which could be observed even when the molar ratio of L-histidine to Cu(II) ion was smaller than unity. The signal for the DNA fibers changed with the orientation of the fibers in the static magnetic field. Based on these results, the signal was assigned to a mono-histidine Cu(II) complex stereospecifically aggregated in a groove or along a phosphodiester chain of the double helical DNA. In contrast to the L-histidine complex, the D-histidine complex bound to DNA did not show such broad signals and the observed spectra for the complex on B-form DNA fibers at -150 degrees C were simulated assuming that the g1 axis of the mono-D-histidine complex tilts by about 55 degrees from the DNA-fiber axis. Addition of some deoxy-nucleotides, but not deoxy-nucleosides, to a solution of a mono-histidine complex resulted in the formation of a dinuclear ternary complex with different structures for L- or D-histidine, suggesting the possibility that the stereospecific aggregation of the L-histidine complex on a double helical DNA was mediated by the phosphodiester backbones.     

Evidence that NiNi acetyl-CoA synthase is active and that the CuNi enzyme is not

The bifunctional CO dehydrogenase/acetyl-CoA synthase (CODH/ACS) plays a central role in the Wood-Ljungdahl pathway of autotrophic CO(2) fixation. One structure of the Moorella thermoacetica enzyme revealed that the active site of ACS (the A-cluster) consists of a [4Fe-4S] cluster bridged to a binuclear CuNi center with Cu at the proximal metal site (M(p)) and Ni at the distal metal site (M(d)). In another structure of the same enzyme, Ni or Zn was present at M(p). On the basis of a positive correlation between ACS activity and Cu content, we had proposed that the Cu-containing enzyme is active [Seravalli, J., et al. (2003) Proc. Natl. Acad. Sci. U.S.A. 100, 3689-3694]. Here we have reexamined this proposal. Enzyme preparations with a wider range of Ni (1.6-2.8) and Cu (0.2-1.1) stoichiometries per dimer were studied to reexamine the correlation, if any, between the Ni and Cu content and ACS activity. In addition, the effects of o-phenanthroline (which removes Ni but not Cu) and neocuproine (which removes Cu but not Ni) on ACS activity were determined. EXAFS results indicate that these chelators selectively remove M(p). Multifrequency EPR spectra (3-130 GHz) of the paramagnetic NiFeC state of the A-cluster were examined to investigate the electronic state of this proposed intermediate in the ACS reaction mechanism. The combined results strongly indicate that the CuNi enzyme is inactive, that the NiNi enzyme is active, and that the NiNi enzyme is responsible for the NiFeC EPR signal. The results also support an electronic structure of the NiFeC-eliciting species as a [4Fe-4S](2+) (net S = 0) cluster bridged to a Ni(1+) (S = (1)/(2)) at M(p) that is bridged to planar four-coordinate Ni(2+) (S = 0) at M(d), with the spin predominantly on the Ni(1+). Furthermore, these studies suggest that M(p) is inserted during cell growth. The apparent vulnerability of the proximal metal site in the A-cluster to substitution with different metals appears to underlie the heterogeneity observed in samples that has confounded studies of CODH/ACS for many years. On the basis of this principle, a protocol to generate nearly homogeneous preparations of the active NiNi form of ACS was achieved with NiFeC signals of approximately 0.8 spin/mol.     

Reaction of nitric oxide with iron bleomycin bound to DNA: properties of the nitrosyl adduct and its reaction with O2

During the ESR spectroscopic titration of nitrosyl-iron bleomycin, ON---Fe(II)Blm, with DNA, its metal domain undergoes a change in environment as the DNA base pair to drug ratio increases to 50 to 1. The ¹⁵N---O stretching frequency of ON---Fe(II)Blm occurs at 1589 cm⁻¹, similar to that for nitrosyl hemoglobin and myoglobin. Upon addition of DNA (3 base pairs per drug molecule), this vibration is substantially broadened. Injection of O₂ into a solution of ON---Fe(II)BlmDNA converts the ESR signal of the nitrosyl species to low spin Fe(III) BlmDNA. NO is largely oxidized to NO₂⁻. The combination of these products suggests that the initial reaction of ON---Fe(II)Blm with O₂ generates Fe(III)Blm and peroxynitrite, O₂NO⁻. If peroxynitrite is formed in the reaction, it does not cause detectable DNA damage. The structural integrity of a supercoiled DNA plasmid, pBR322, is not compromised and no base propenals are produced during this reaction.     

Coppier ion-dependent oxy-radical mediated DNA damage from dihydroxy derivative of etoposide

The dihydroxy etoposide, a metabolite of the clinically active anticancer drug, VP-16, induced extensive DNA damage in the presence of copper ions. While superoxide dismutase was without any effect on the DNA damage, catalase and inhibitors of free hydroxyl radicals inhibited the DNA degradation, indicating that hydroxyl radicals were responsible for this drug-Cu-dependent DNA damage.     

Interaction between low-affinity cupric ion and human methemoglobin

Human hemoglobin has been shown to contain a high- as well as a low-affinity binding site for cupric ion on each of its constitutent beta chains. The copper that is bound to the low-affinity site has been implicated in the selective oxidation of the beta hemes. In the present work a low-affinity binding site for cupric ion has been located within 10 A of the heme iron in human hemoglobin. It is suggested that the proximal histidine is involved in the binding of copper at this site and that it participates in the oxidation of heme iron and reduction of cupric ion.     

Spectral, kinetic, and thermodynamic properties of Cu(I) and Cu(II) binding by methanobactin from Methylosinus trichosporium OB3b

To examine the potential role of methanobactin (mb) as the extracellular component of a copper acquisition system in Methylosinus trichosporium OB3b, the metal binding properties of mb were examined. Spectral (UV-visible, fluorescence, and circular dichroism), kinetic, and thermodynamic data suggested copper coordination changes at different Cu(II):mb ratios. Mb appeared to initially bind Cu(II) as a homodimer with a comparatively high copper affinity at Cu(II):mb ratios below 0.2, with a binding constant (K) greater than that of EDTA (log K = 18.8) and an approximate DeltaG degrees of -47 kcal/mol. At Cu(II):mb ratios between 0.2 and 0.45, the K dropped to (2.6 +/- 0.46) x 10(8) with a DeltaG degrees of -11.46 kcal/mol followed by another K of (1.40 +/- 0.21) x 10(6) and a DeltaG degrees of -8.38 kcal/mol at Cu(II):mb ratios of 0.45-0.85. The kinetic and spectral changes also suggested Cu(II) was initially coordinated to the 4-thiocarbonyl-5-hydroxy imidazolate (THI) and possibly Tyr, followed by reduction to Cu(I), and then coordination of Cu(I) to 4-hydroxy-5-thiocarbonyl imidazolate (HTI) resulting in the final coordination of Cu(I) by THI and HTI. The rate constant (k(obsI)) of binding of Cu(II) to THI exceeded that of the stopped flow apparatus that was used, i.e., >640 s(-)(1), whereas the coordination of copper to HTI showed a 6-8 ms lag time followed by a k(obsII) of 121 +/- 9 s(-)(1). Mb also solubilized and bound Cu(I) with a k(obsI) to THI of >640 s(-)(1), but with a slower rate constant to HTI (k(obsII) = 8.27 +/- 0.16 s(-)(1)), and appeared to initially bind Cu(I) as a monomer.