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PubMed2002

A systematic screening of total antioxidants in dietary plants.

A predominantly plant-based diet reduces the risk for development of several chronic diseases. It is often assumed that antioxidants contribute to this protection, but results from intervention trials with single antioxidants administered as supplements quite consistently do not support any benefit. Because dietary plants contain several hundred different antioxidants, it would be useful to know the total concentration of electron-donating antioxidants (i.e., reductants) in individual items. Such data might be useful in the identification of the most beneficial dietary plants. We have assessed systematically total antioxidants in a variety of dietary plants used worldwide, including various fruits, berries, vegetables, cereals, nuts and pulses. When possible, we analyzed three or more samples of dietary plants from three different geographic regions in the world. Total antioxidants was assessed by the reduction of Fe(3+) to Fe(2+) (i.e., the FRAP assay), which occurred rapidly with all reductants with half-reaction reduction potentials above that of Fe(3+)/Fe(2+). The values, therefore, expressed the corresponding concentration of electron-donating antioxidants. Our results demonstrated that there is more than a 1000-fold difference among total antioxidants in various dietary plants. Plants that contain most antioxidants included members of several families, such as Rosaceae (dog rose, sour cherry, blackberry, strawberry, raspberry), Empetraceae (crowberry), Ericaceae (blueberry), Grossulariaceae (black currant), Juglandaceae (walnut), Asteraceae (sunflower seed), Punicaceae (pomegranate) and Zingiberaceae (ginger). In a Norwegian diet, fruits, berries and cereals contributed 43.6%, 27.1% and 11.7%, respectively, of the total intake of plant antioxidants. Vegetables contributed only 8.9%. The systematic analysis presented here will facilitate research into the nutritional role of the combined effect of antioxidants in dietary plants.

Antioxidants↗
PubMed1999

Formation of 5-formyl-2'-deoxycytidine from 5-methyl-2'-deoxycytidine in duplex DNA by Fenton-type reactions and gamma-irradiation.

5-methyl-2'-deoxycytidine (5-Me-dC) is formed by the enzymatic methylation of dC, primarily in CpG sequences in DNA, and is involved in the regulation of gene expression. In the present study, 5-Me-dC and double-stranded DNA fragments containing 5-Me-dC were either gamma-irradiated or aerobically treated with Fenton-type reagents, Fe(II)-EDTA, Fe(II)-nitrilotriacetic acid, Fe(III)-EDTA-H(2)O(2)-catechol or ascorbic acid-H(2)O(2) under neutral conditions. The formation of 5-formyl-2'-deoxycytidine (5-CHO-dC) was observed upon treatment of both 5-Me-dC and DNA fragments containing 5-Me-dC. The yields of 5-CHO-dC from 5-Me-dC and those of 5-formyl-2'-deoxyuridine from dT were comparable. These results suggest that 5-Me-dC in DNA is as susceptible to oxidation as dT in cells, and raise the possibility that 5-CHO-dC may contribute to the high mutagenic rate observed in CpG sequences in genomic DNA.

Ascorbic Acid↗
PubMed1977

Reaction of chlorocruorin with heme iron ligands and carbonyl reagents.

Chlorocruorin was purified from Potamilla leptochaeta and the spectral properties of its derivatives wwere investigated. Ferri- or ferrochlorocruorin did not exhibits a ferrihemochrome or ferrohemochrome spectrum, respectively. Oxy- and carbonmonoxy-ferrochlorocruorin did show ferrohemochrome-type spectra. Ferrihemochromes were formed, however, when oxy-or ferrichlorocruorin was treated with 0.02-0.05% SDS, and they were transformed to ferrohemochromes by reduction with sodium dithionite. Ferrihemochrome formation was also brought about by increasing the pH of a ferrichlorocruorin solution to 9, or by liganding of extrinsic imidazole or cyanide to the ferric pigment. Therefore, it is apparent that at least one of the coordination positions on the heme iron in ferri-and ferrochlorocruorin is vacant or occupied by a weak-field ligand. Titration studies of ferrichlorocruorin with imidazole indicated that this supposedly vacant coordination position was occupied first by the imidazole, and that the intrinsic ligand of protein orgin was replaced finally at higher concentrations. The extrinsic ligands in the cyanide and imidazole complexes of ferrichlorocruorin were excluded from their coordination positions as the protein moiety assumed conformations inherent to the reduced pigment. Spectral analyses indicated that the intrinsic ligand is an imidazole moiety of a histidyl residue. When chlorocruorin was intact, carbonyl reagents such as cyanide and sodium bisulfite did not add to the formyl group of chlorocruoreheme. When the protein conformation was perturbed by SDS, addition to ferrichlorocruorin occurred appreciably. This addition was accelerated if the heme iron coordination position had been occupied by strong field ligands,and was reversed to some extent as the chlorocruorin complexes were reduced.

Cyanides↗
PubMed1987

Iron uptake by the yeast Saccharomyces cerevisiae: involvement of a reduction step.

Among several parameters affecting the rate and amount of iron uptake by Saccharomyces cerevisiae, the oxidation state of iron appeared to be determinant. Iron presented as Fe(II) was taken up faster than Fe(III) and the kinetic parameters were different. Iron was taken up by the cells from different ferric chelates, at rates that did not depend on their stability constants, and uptake was strongly inhibited by an iron(II)-trapping reagent like ferrozine. Iron was physiologically reduced by a transplasmamembrane redox system, which was induced in iron-deficient conditions. We propose that iron must be reduced to be taken up by the cells in the same way as other divalent cations.

Biological Transport↗
PubMed1975

Enterobacterial chelators of iron: their occurrence, detection, and relation to pathogenicity.

In or on agar media, low-density seedings of enterobacteria fail to grow in the presence of certain concentrations of ethylene diamine-di-orthohydroxyphenyl acetic acid (EDDA); on the other hand, high-density seedings not only grow but secrete iron chelators which release the iron bound by the EDDA in the medium and stimulate the growth of low-density seedings. Plates of media containing EDDA with low-density seedings of indicator organisms were used to survey iron-chelator production in seven enterobacterial genera, including a number of virulent smooth (S) forms from which rough (R) mutants had been obtained. An examination of over 80 strains of Aeromonas, Escherichia, Klebsiella, Proteus, Pseudomonas, Salmonella and Shigella species indicated that the iron chelators from bacteria in all these genera were functionally interchangeable. Chelator production was equally good with randomly selected avirulent and virulent strains of Klebsiella spp. and E. coli; and with the S forms and their avirulent R mutants in one pair of escherichiae, six pairs of salmonellae (4 species) and six pairs of shigellae (3 species). As determinable in vitro, the capacity to synthesise iron chelators is clearly no index of the capacity of a strain to proliferate in vivo.

Aeromonas↗
PubMed1993

Inactivation of enzymes of the glutathione antioxidant system by treatment of cultured human keratinocytes with peroxides.

Either metal ions, H2O2, t-butyl hydroperoxide (tBHP), or cumene hydroperoxide (CHP) was added to the medium of cultured human keratinocytes, and the activities of key peroxide-metabolizing enzymes were examined in a sonicated cell supernatant from the treated cells. 200 microM Fe++ +200 microM Fe was without effect on any enzyme activity. 700 microM CHP or tBHP decreased glutathione (GSH) peroxidase activity by 90% after 5 h and by 100% at 20 h, even if the CHP or tBHP was removed from the media after 90 min. H2O2 at 700 microM caused a brief 17% decrease in activity, which was followed by complete recovery. GSH peroxidase was found to be rapidly inactivated in vitro by CHP, but the enzyme was also inactivated at 37 degrees C even in the absence of CHP. GSH prevented both types of inactivation. Consistent with this in vitro data, in vivo depletion of the GSH pool with buthionine sulfoximine led to lower levels of GSH peroxidase and increased sensitivity to peroxide-induced inactivation. Neither GSH reductase nor GSH S-transferase were inactivated by any treatment although CHP did cause a small increase in the activity of the latter, which was not due to induction. The activity of glucose-6-phosphate dehydrogenase was decreased 50% following treatment for 5 h with 700 microM CHP or tBHP, whereas H2O2 treatment caused a brief 15% decline, followed by recovery. The effects of peroxides were not altered by changing the concentration of Ca++ in the media. Catalase was unaffected by concentrations of peroxide up to 700 microM. Inhibition of catalase with aminotriazole slightly enhanced the toxicity of 700 microns H2O2. In summary, organic hydroperoxides at relatively low concentrations inactive key enzymes of the glutathione pathway, but hydrogen peroxide does not.

Antimetabolites↗
PubMed1994

Ferric iron reduction-linked growth yields of Shewanella putrefaciens MR-1.

The anaerobic reduction of ferric citrate by Shewanella putrefaciens MR-1 cells was inhibited markedly by p-chloromercuriphenylsulphonate, moderately by potassium cyanide, and to a small extent by 2-heptyl-4-hydroxyquinolone-N-oxide. Iron reduction was accompanied by increases in total cellular protein, with values of 0.33-7.54 g cell protein produced per mol Fe(III) reduced. The growth yields were dependent upon the growth conditions of the inoculum and the initial concentration of Fe(III) citrate in the medium. Specifically, maximum growth yields were obtained when the inoculum was pregrown anaerobically and when the initial Fe(III) citrate concentrations were 5-10 mmol l-1. Lower growth yields were obtained with initial Fe(III) citrate concentrations of 20-30 mmol l-1, suggesting that cell growth was partially inhibited by higher concentrations of Fe(III) or Fe(II). Maximal growth yields were also observed early (6-24 h), after which continued increases in cell protein were minimal.

Anaerobiosis↗
PubMed1978

Formation of complexes between microsomal cytochrome P-450-Fe(II) and nitrosoarenes obtained by oxidation of arylhydroxylamines or reduction of nitroarenes in situ.

A cytochrome P-450 complex exhibiting a Soret peak at 454 nm is formed by direct interaction of nitrosobenzene with NADPH-reduced rat liver microsomes in anaerobic conditions, by reaction of phenylhydroxylamine with aerobic microsomes or during nitrobenzene reduction by NADPH-reduced or dithionite-reduced microsomes. In the latter conditions, the complex formation is only transient as it is unstable to dithionite. Analogous reactions with myoglobin lead to the previously described myoglobin-Fe(II)-nitrosobenzene complex which has similar properties to those of the 454-nm-absorbing cytochrome P-450 complex. This analogy, together with the various conditions of its formation, strongly indicates that it is a cytochrome-P-450-Fe(II)-nitrosobenzene complex. The corresponding complex with the 4-chloro-nitrosobenzene ligand is formed in similar conditions. Cytochrome P-450-Fe(II) complexes with nitrosoarenes seem less stable than the previously described complexes with nitrosoalkanes.

Animals↗
PubMed1990

The complex formed between plastocyanin and cytochrome c. Investigation by NMR spectroscopy.

Spinach plastocyanin and horse heart cytochrome c have been shown, by monitoring the behaviour of the hyperfine-shifted heme resonances of Fe(III) cytochrome c on titration with Cu(II) plastocyanin, to form a 1:1 complex with a dissociation constant of 67 mM (D2O, pH* 7.0, 300 K). The interaction sites on the plastocyanin surface have been investigated in one- and two-dimensional NMR experiments involving competition for plastocyanin between cytochrome c and the paramagnetic cation Cr(NH3)(3+)6. The plastocyanin resonances which are paramagnetically broadened in the spectrum of plastocyanin alone are also broadened in the spectrum of the mixture of the two proteins. This shows that, on the NMR time scale, no plastocyanin residues are hidden from Cr(NH3)(3+)6 by complexation with cytochrome c. [It has been shown that Cr(NH3)(3+)6 does not disrupt formation of the complex between the two proteins.] It appears that initial complexation of cytochrome c takes place at the acidic east site of plastocyanin, and that the extensive negative electrostatic surface of plastocyanin accommodates the paramagnetic probe and cytochrome c simultaneously in a dynamic ternary complex. The location of the electron transfer site on plastocyanin is discussed.

Animals↗
PubMed1993

Abduction of iron(III) from the soluble methane monooxygenase hydroxylase and reconstitution of the binuclear site with iron and manganese.

The apo-form of the soluble methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath) was prepared via chelation of iron(III) with 3,4-dihydroxybenzaldehyde. The apohydroxylase was reconstituted by the anaerobic addition of Fe(II) followed by air oxidation. The enzyme thus prepared regained 85-90% of its original catalytic activity. The incorporation of two manganese(II) ions/mol of apohydroxylase was monitored by EPR spectroscopy. The Mn(II) ions occupy the native diiron active site and remain in the +2 oxidation state. The EPR data suggest strong coupling between the two Mn(II) ions and retention of the mu-hydroxo (alkoxo) bridge. The results of this study indicate that the M. capsulatus (Bath) hydroxylase contains a single diiron site.

Apoenzymes↗
PubMed1994

Reactions of prostaglandin H synthase with monosubstituted hydrazines and diazenes. Formation of iron(II)-diazene and iron(III)-sigma-alkyl or iron(III)-sigma-aryl complexes.

The reaction of p-chlorophenylhydrazine with prostaglandin H synthase (PGHS) Fe(III) under aerobic conditions leads to a partial destruction of the heme and to a new complex absorbing at 436 nm. This complex is also obtained by reaction of p-chlorophenyldiazene (pClPhN = NH) with PGHS Fe(III) under anaerobic conditions and by oxidation of the PGHS Fe(II)(pClPhN = NH) diazene complex by Fe(CN)6K3. The similarity between those reactions and those of arylhydrazines and aryldiazenes with other hemoproteins such as cytochrome P450 and hemoglobin and myoglobin, as well as the similarities between the spectroscopic and chemical properties of this complex and those of the sigma-aryl complexes of other hemoproteins such as hemoglobin and myoglobin, strongly suggested a PGHS Fe(III)-pClPh structure for this complex. It was completely established after the extraction of its heme, by butan-2-one at 0 degree C under neutral or acidic conditions, which led to the sigma-aryl PGHS-Fe(III)-pClPh complex and to N-phenylprotoporphyrin IX, respectively. A mechanism is proposed for the formation of the PGHS Fe(III) pClPh complex; it includes the reduction of PGHS Fe(III) into PGHS Fe(II) with formation of the diazene pClPhN = NH. This diazene can bind to PGHS Fe(II) or be oxidized with formation of pClPh free radicals. These radicals can react with PGHS Fe(II) to form the PGHS Fe(III)-pClPh complex or with the protein, or may initiate free radical oxidations which could lead to destruction of the heme or of the protein. Other alkylhydrazines or arylhydrazines also react with PGHS Fe(III) under aerobic conditions with the formation of PGHS Fe(III)-R or aryl (Ar) complexes and heme destruction. Alkylhydrazines such as methylhydrazine, which lead to very reactive alkyl radicals, lead to very low amounts of PGHS Fe(III)-R complex and high amounts of heme destruction, whereas arylhydrazines bearing electron-withdrawing substituents such as 3,4-dichlorophenylhydrazine, which lead to stabilized aryl radicals, lead to a high amounts of PGHS Fe(III)-Ar complex and low amounts of heme destruction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Comparative study on the selective chalcopyrite bioleaching of a molybdenite concentrate with mesophilic and thermophilic bacteria.

This study evaluates different bioleaching treatments of a molybdenite concentrate using mesophilic and thermophilic bacterial cultures. Further studies on the chemical leaching and the electrochemical behavior of the MoS(2) concentrate were carried out. Bioleaching tests showed a progressive removal of chalcopyrite from the molybdenite concentrate with an increase in temperature. Chemical leaching tests support the idea of an indirect attack of the concentrate. Electrochemical tests indicate that chalcopyrite dissolution is favored when molybdenite is present. Therefore, this type of bioleaching treatment could be applied to purify molybdenite flotation concentrates by selectively dissolving chalcopyrite.

Bacteria↗
PubMed2005

Antioxidant properties of carnosine re-evaluated with oxidizing systems involving iron and copper ions.

Carnosine has antioxidant properties and is efficient in the treatment of chemically-induced inflammatory lesions in animals. However, some studies question its biological significance as antioxidant and show lack of protection and even pro-oxidant effect of carnosine in systems containing nickel and iron ions. The ability of carnosine to: (1) reduce Fe(3+) into Fe(2+) ions; (2) protect deoxyribose from oxidation by Fe(2+)-, Fe(3+)-, and Cu(2+)-H(2)O(2)-EDTA systems; (3) protect DNA from damage caused by Cu(2+)-, and Fe(2+)-H(2)O(2)-ascorbate systems; (4) inhibit HClO- and H(2)O(2)-peroxidase-induced luminol dependent chemiluminescence was tested in vitro. At concentration 10 mM carnosine reduced 16.6+/-0.5 nmoles of Fe(3+) into Fe(2+) ions during 20 min. incubation and added to plasma significantly increased its ferric reducing ability. Inhibition of deoxyribose oxidation by 10 mM carnosine reached 56+/-5, 40+/-11 and 30+/-11% for systems containing Fe(2+), Fe(3+) and Cu(2+) ions, respectively. The damage to DNA was decreased by 84+/-9 and 61+/-14% when Cu(2+)-, and Fe(2+)-H(2)O(2)-ascorbate systems were applied. Combination of 10 mM histidine with alanine or histidine alone (but not alanine) enhanced 1.3 and 2.3 times (P<0.05) the DNA damage induced by Fe(2+)-H(2)O(2)-ascorbate. These amino acids added to 10 mM carnosine decreased 3.1-fold (P<0.05) its protective effect on DNA. Carnosine at 10 and 20 mM decreased by more than 90% light emission from both chemiluminescent systems. It is concluded that carnosine has significant antioxidant activity especially in the presence of transition metal ions. However, hydrolysis of carnosine with subsequent histidine release may be responsible for some pro-oxidant effects.

Animals↗
PubMed2001

Vitamin C-induced decomposition of lipid hydroperoxides to endogenous genotoxins.

Epidemiological data suggest that dietary antioxidants play a protective role against cancer. This has led to the proposal that dietary supplementation with antioxidants such as vitamin C (vit C) may be useful in disease prevention. However, vit C has proved to be ineffective in cancer chemoprevention studies. In addition, concerns have been raised over potentially deleterious transition metal ion-mediated pro-oxidant effects. We have now determined that vit C induces lipid hydroperoxide decomposition to the DNA-reactive bifunctional electrophiles 4-oxo-2-nonenal, 4,5-epoxy-2(E)-decenal, and 4-hydroxy-2-nonenal. The compound 4,5-Epoxy-2(E)-decenal is a precursor of etheno-2'-deoxyadenosine, a highly mutagenic lesion found in human DNA. Vitamin C-mediated formation of genotoxins from lipid hydroperoxides in the absence of transition metal ions could help explain its lack of efficacy as a cancer chemoprevention agent.

Aldehydes↗
PubMed2001

Application of the Marcus cross relation to hydrogen atom transfer reactions.

The transfer of a hydrogen atom-a proton and an electron-is a fundamental process in chemistry and biology. A variety of hydrogen atom transfer reactions, involving iron complexes, phenols, hydroxylamines, tBuOOH, toluene, and related radicals, are shown to follow the Marcus cross relation. Thus, the Marcus theory formalism based on ground-state energetics and self-exchange rates, originally developed for electron transfer processes, is also valuable for hydrogen atom transfer. Compounds that undergo slow proton transfer (C-H bonds) or slow electron transfer (cobalt complexes) also undergo slow hydrogen atom transfer. Limitations of this approach are also discussed.

Chemical Phenomena↗