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PubMedDate not supplied

Comparative study of intravenous ascorbic acid versus low-dose desferroxamine in patients on hemodialysis with hyperferritinemia.

BACKGROUND: In patients on hemodialysis (HD), parenteral iron improves the response to recombinant human erythropoietin (rhuEPO) therapy, but in some subjects it produces an iron overload, increasing their morbidity and mortality rates. In these cases, iron administration must be discontinued. This study aimed to investigate the efficiency of treatment with ascorbic acid (AA) or desferroxamine (DFO) to mobilize and reduce iron stores, and to determine the effect of these compounds on erythropoiesis. METHODS: We performed a prospective and randomized trial over 6 months, which included 27 patients with serum ferritin levels >800 ng/mL, TSAT >30% and stabilized hemoglobin (Hb) and rhuEPO doses. All patients had previously received parenteral iron (Ferlecit). Nine patients received 200 mg of intravenous (i.v.) AA 3 times/week and nine patients received 1 mg/Kg/week of DFO; the remaining nine patients were the control group. RESULTS: There were no significant differences in iron loss or mobilization due to dialysis. When Ferlecit was discontinued, functional iron did not vary and the epoetin resistance index (rhuEPO dose/Hb) was reduced by 21% in the i.v. AA group. In the DFO and control groups, functional iron levels fell. In the DFO group the epoetin resistance index increased by 20%, with no modifications in the control group. There was a positive correlation between transaminases and serum ferritin. CONCLUSIONS: In HD patients with an iron overload, neither i.v. AA administration or low-dose DFO increased iron mobilization or iron loss due to dialysis. I.v. AA administration allows elimination of iron from stores without any drop in the functional iron produced by discontinuing parenteral maintenance iron; it also improves the response to rhuEPO. DFO did not elicit any positive effects on erythropoiesis.

Aged↗
PubMed1992

Pharmacokinetics of aluminoxamine and ferrioxamine and dose finding of desferrioxamine in haemodialysis patients.

We investigated the pharmacokinetics of desferrioxamine and its chelated compounds aluminoxamine and ferrioxamine in normal volunteers and haemodialysis patients with and without iron overload. Desferrioxamine was administered in a single dose of 30 mg per kg body-weight was a 30-min infusion to five healthy volunteers and to 20 haemodialysis patients (five patients without haemosiderosis and 15 patients with haemosiderosis). The interdialytic half-life of ferrioxamine was 2.2 h in normal volunteers, 13.3 h in dialysis patients without haemosiderosis, and 24.6 h in patients with haemosiderosis. There was no interdialytic elimination of aluminoxamine. In a second study, seven dialysis patients received 5, 10, and 20 mg per kg body-weight desferrioxamine in a random order with a time interval of 2 weeks. The peak serum concentrations after these doses were 4.1 +/- 2.9, 6.4 +/- 2.9, and 10.7 +/- 7.1 mumol/l for ferrioxamine and 2.8 +/- 1.5, 3.1 +/- 1.5, and 4.2 +/- 1.7 mumol/l for aluminoxamine. Thus, a 4-fold increase in desferrioxamine dosage resulted in a 2.7-fold increase in peak ferrioxamine levels and in only a 1.5-fold increase in peak aluminoxamine levels. We conclude that dialysis patients, especially those with haemosiderosis, are exposed to persistently elevated ferrioxamine levels. Weekly doses of 5-10 mg/kg of desferrioxamine would be sufficient for aluminium chelation therapy.

Adult↗
PubMed2001

Detection of experimental hepatic tumors using long circulating superparamagnetic particles.

RATIONALE AND OBJECTIVES: To evaluate the potential of an iron oxide-based MR contrast agent for the detection and delineation of experimental liver tumors during the early vascular phase of the compound. METHODS: Superparamagnetic blood pool agent (SBPA) was administered intravenously to rabbits bearing VX2 tumors. Images were acquired before the injection, immediately after, and 1 or 3 weeks later. The variations of signal intensity were measured in the tumors and in several tissues for various T1-weighted spin-echo, T2-weighted fast spin-echo, and T2-weighted gradient-recalled-echo sequences. RESULTS: Fourteen and 12 of the 16 tumors were detected immediately after SBPA injection using, respectively, the T2-weighted fast spin-echo and T2-weighted gradient-recalled-echo sequences. A significant decrease in signal intensity was observed in well-perfused organs, and blood signal was abolished even at the lowest injected dose and using a T1-weighted sequence. In the late phase, the loss in signal intensity of the liver was even more pronounced. CONCLUSION: The dominant T2 effect of SBPA induces an increase in the tumor-to-liver and tumor-to-blood contrast during the vascular phase, improving the detection of the tumors and allowing the distinction between small lesions and vessels through plane. This effect on the liver signal persists for several days because of the incorporation of SBPA in the reticuloendothelial system.

Animals↗
PubMedDate not supplied

Hydrous pyrolysis of polycyclic aromatic hydrocarbons and implications for the origin of PAH in hydrothermal petroleum.

Polycyclic aromatic hydrocarbons (PAH) are found at high concentrations in thermally altered organic matter and hydrothermally generated petroleum from sediment-covered seafloor hydro-thermal systems. To better understand the factors controlling the occurrence of PAH in thermally altered environments, the reactivities of two PAH, phenanthrene and anthracene, were investigated in hydrothermal experiments. The compounds were heated with water at 330 degrees C in sealed reaction vessels for durations ranging from 1 to 17 days. Iron oxide and sulfide minerals, formic acid, or sodium for-mate were included in some experiments to vary conditions within the reaction vessel. Phenanthrene was unreactive both in water alone and in the presence of minerals for up to 17 days, while anthracene was partially hydrogenated (5-10%) to di- and tetrahydroanthracene. In the presence of 6-21 vol % formic acid, both phenanthrene and anthracene reacted extensively to form hydrogenated and minor methylated derivatives, with the degree of hydrogenation and methylation increasing with the amount of formic acid. Phenanthrene was slightly hydrogenated in sodium formate solutions. The hydrogenation reactions could be readily reversed; heating a mixture of polysaturated phenanthrenes resulted in extensive dehydrogenation (aromatization) after 3 days at 330 degrees C. While the experiments demonstrate that reaction pathways for the hydrogenation of PAH under hydrothermal conditions exist, the reactions apparently require higher concentrations of H2 than are typical of geologic settings. The experiments provide additional evidence that PAH may be generated in hydrothermal systems from progressive aromatization and dealkylation of biologically derived polycyclic precursors such as steroids and terpenoids. Furthermore, the results indicate that PAH initially present in sediments or formed within hydrothermal systems are resistant to further thermal degradation during hydrothermal alteration.

Anthracenes↗
PubMed2000

Use of ultrafiltration and chromatography to assess aluminum speciation in serum after deferoxamine administration.

Deferoxamine effectively chelates aluminum by forming aluminoxamine, a low-molecular-weight compound removable by dialysis. However, aluminum-bound species other than aluminoxamine might be present in serum after the administration of deferoxamine. To study aluminum speciation after the administration of deferoxamine, high-performance liquid chromatography (HPLC) and ultrafiltration techniques were used. Samples of serum were obtained from six dialysis patients 44 hours after the administration of a single dose of deferoxamine. HPLC and ultrafiltration studies were performed. In the HPLC studies, samples underwent ultrafiltration, the filtrate was injected into the chromatographic system, and detection was performed by UV light and atomic absorption spectrometry. Unknown species of aluminum other than aluminoxamine were found in the early elution fractions. In the ultrafiltration studies, the same samples of serum from the six patients underwent ultrafiltration using membranes with different molecular-weight cutoff values from 1 to 30 kd. The percentages of aluminum found by ultrafiltration using membranes with cutoff values of 5, 10, and 30 kd were greater (64.4% +/- 2.5%, 63.5% +/- 3.7%, and 65.6% +/- 4.3%, respectively) than the percentages obtained with membranes with a 1-kd cutoff value (38.7%), suggesting that the unknown species of aluminum have a molecular weight between 1 and 5 kd. The unknown species of aluminum cannot be aluminoxamine because they behaved in a different way with HPLC.

Aluminum↗
PubMed1998

Mutagenicity of p-aminophenol in E. coli WP2uvrA/pKM101 and its relevance to oxidative DNA damage.

It was recently reported that p-aminophenol (p-AP) induces DNA cleavage in mouse lymphoma cells, CHO cells and human lymphoblastoid cells. The mutagenicity of p-AP has not, however, been detected by reverse mutation assays. The purpose of this study was to assess the mutagenicity of p-AP by reverse mutation assay using Escherichia coli WP2uvrA/pKM101, which has a spectrum for detecting mutations different from those of other strains in the family with an AT base pair at the mutation site and has higher sensitivity to certain oxidative mutagens as compared to other strains. We found that p-AP was mutagenic to E. coli WP2uvrA/pKM101. The mutagenic activity of this compound was suppressed with the addition of dimethylsulfoxide or catalase, suggesting the involvement of active oxygen species in the mutagenic process induced by p-AP. To further elucidate the underlying mechanism, we used isolated DNA for the following experiments. It was revealed, by gel electrophoretic analysis, that p-AP induced DNA cleavage in the presence of Fe(III). However, p-AP alone did not induce this cleavage. Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine by p-AP in calf thymus DNA was also detected in the presence of Fe(III) by HPLC with an electrochemical detector. ESR-spin trapping experiments using DMPO detected the production of hydroxyl radical (.OH) in the solution of p-AP with Fe(III). Both p-AP mediated DNA damages and .OH production by p-AP in the presence of Fe(III) were completely inhibited by .OH scavengers (ethanol, mannitol, sodium formate, dimethylsulfoxide) and catalase. These results suggest that .OH derived from the reaction between H2O2 and Fe(III) (Fenton reaction) participates in the oxidative DNA damage. Accordingly, the same mechanism might be working in E. coli WP2uvrA/pKM101 during induction of the mutation by p-AP.

Adenosine Triphosphatases↗
PubMed1999

Stabilized polynuclear iron hydroxide is an efficient oral phosphate binder in uraemic patients.

BACKGROUND: There is a continuing need for non-aluminium and non-calcium-containing oral phosphate binders. A novel product, i.e. stabilized polynuclear iron hydroxide, has experimentally been shown to be an effective phosphate binder. The purpose of the study was to test the efficacy and tolerability of the compound in hyperphosphataemic patients with stable preterminal renal failure. METHODS: In an open uncontrolled study we examined a total of 13 patients with stable preterminal renal failure (median serum-creatinine 5.4 mg/dl, range 4.2-7.3 mg/dl) and hyperphosphataemia (median fasting plasma-Pi 2.2 mmol/l, range 1.95 3.0 mmol/l). Patients were given dietary advise to maintain a constant intake of phosphate and this was verified by measuring urinary Pi excretion. After 2 weeks on no oral phosphate binders, patients were given daily 3 x 2.5 g stabilized polynuclear iron hydroxide with meals for 4 weeks. In a blinded fashion plasma-Pi and urinary-Pi as well as 1,84 i-PTH, vitamin D metabolites, serum-iron and ferritin were measured in a central laboratory. RESULTS: Compared to baseline (no oral phosphate binders), the median per cent decrease of fasting plasma-Pi at day 14 was 20% (7.2-41%) (P<0.001 by Wilcoxon test) and the median per cent decrease of urinary P excretion was 37% (9.6-56.6%) (P<0.0003 by Wilcoxon test for paired differences). Ferritin levels did not differ significantly during the study. Apart from a certain laxative action and black discolouration of the faeces, no side effects were noted in this short-term study. CONCLUSION: Stabilized polynuclear iron hydroxide is a promising, efficaceous and well tolerated phosphate binder.

Administration, Oral↗
PubMed2001

Investigating the structural and electronic properties of nitrile hydratase model iron(III) complexes using projected unrestricted Hartree-Fock (PUHF) calculations.

Important structural and mechanistic details concerning the non-heme, low-spin Fe(III) center in nitrile hydratase (NHase) remain poorly understood. We now report projection unrestricted Hartree-Fock (PUHF) calculations on the spin preferences of a series of inorganic complexes in which Fe(III) is coordinated by a mixed set of N/S ligands. Given that many of these compounds have been prepared as models of the NHase metal center, this study has allowed us to evaluate this computational approach as a tool for future calculations on the electronic structure of the NHase Fe(III) center itself. When used in combination with the INDO/S semiempirical model, the PUHF method correctly predicts the experimentally observed spin state for 12 of the 13 Fe(III)-containing complexes studied here. The one compound for which there is disagreement between our theoretical calculations and experimental observation exhibits temperature-dependent spin behavior. In this case, the failure of the PUHF-INDO/S approach may be associated with differences between the structure of the Fe(III) complex present under the conditions used to measure the spin preference and that observed by X-ray crystallography. A preliminary analysis of the role of the N/S ligands and coordination geometry in defining the Fe(III) spin preferences in these complexes has also been undertaken by computing the electronic properties of the lowest energy Fe(III) spin states. While any detailed interpretation of our results is constrained both by the limited set of well-characterized Fe(III) complexes used in this study and by the complicated dependence of Fe(III) spin preference upon metal-ligand interactions and coordination geometry, these PUHF-INDO/S calculations support the hypothesis that the deprotonated amide nitrogens coordinating the metal stabilize the low-spin Fe(III) ground state seen in NHase. Strong evidence that the sulfur ligands exclusively define the Fe(III) spin state preference by forming metal-ligand bonds with significant covalent character is not provided by these computational studies. This might, however, reflect limitations in modeling these systems at the INDO/S level of theory.

Computer Simulation↗
PubMed1998

Sodium iron EDTA [NaFe(III)EDTA] as a food fortificant does not influence absorption and urinary excretion of manganese in healthy adults.

NaFe(III)EDTA is a promising iron (Fe) compound for food fortification programs because of its high Fe bioavailability from meals containing dietary inhibitors of Fe absorption such as phytic acid. However, this Fe compound is not currently used in any large-scale fortification program because of concern over its possible negative influence on the metabolism of other essential minerals or its possible influence on the absorption of potentially toxic elements, such as manganese (Mn). In this study, Mn absorption and urinary excretion were studied in adults after intake of an Fe-fortified weaning cereal labeled with 54Mn. In a crossover design, the fortification of the weaning cereal with Fe as NaFeEDTA was compared with ferrous sulfate. Manganese absorption was measured by extrapolation from whole-body retention data 10-30 d after intake, and urinary excretion of 54Mn was measured over 7 d. No significant differences in 54Mn absorption or urinary excretion were found; 1.1 +/- 0.15 and 0.91 +/- 0.35% of the ingested dose was absorbed from the cereal fortified with NaFe(III)EDTA and FeSO4, respectively. Urinary excretion of 54Mn was very low; the total radioactivity in urine represented 1.1 +/- 0.55% of the absorbed dose with NaFe(III)EDTA and 0.72 +/- 0.53% of the absorbed dose with FeSO4. Until now, Fe-fortification programs have met with only limited success. The introduction of NaFeEDTA as a food fortificant could be a useful tool to provide bioavailable Fe to vulnerable groups in the population and thus aid in combating Fe deficiency.

Absorption↗
PubMed1984

Hemoglobin. A biologic fenton reagent.

Iron and iron compounds may facilitate hydroxyl-radical generation from activated oxygen species. Earlier work on the generation of this radical has been focused on simple, low-molecular-weight iron compounds. We hypothesized that free hemoglobin, like other iron-rich substances, might also mediate hydroxyl-radical generation. We find: 1) In the presence of a superoxide anion-generating system (hypoxanthine and xanthine oxidase), hemoglobin promotes hydroxyl-radical formation in a dose-dependent fashion. 2) This generation of hydroxyl radical is greatly decreased by prior oxidation of the hemoglobin, equilibration of hemoglobin with carbon monoxide, or addition of catalase, while added superoxide dismutase has little effect. Therefore, hydroxyl radical probably arises primarily via reaction between the ferrous heme iron and H2O2. 3) In further support of this, hydroxyl radical forms as readily upon the addition of H2O2 to hemoglobin. 4) Hemoglobin also increases hypoxanthine/xanthine oxidase-driven peroxidation of poly-unsaturated fatty acids such as arachidonic acid and human red cell membrane lipids. 5) The addition of sufficient haptoglobin (the plasma hemoglobin-binding protein) suppresses both hemoglobin-driven hydroxyl radical and malondialdehyde generation. Thus, free hemoglobin may be biologically hazardous, in part because it acts as a "Fenton" reagent, having the potential to catalyze hydroxyl-radical generation in areas of inflammation. Haptoglobin, which binds hemoglobin very tightly, blocks this through a presently unknown mechanism. An important physiologic function of haptoglobin may be prevention of such hemoglobin-mediated oxidation.

Arachidonic Acid↗
PubMed2004

Effects of in vitro glycation on Fe3+ binding and Fe3+ isoforms of transferrin.

BACKGROUND: In diabetes, protein function is altered by glycation, but the impact on the Fe3+ binding and antioxidant functions of transferrin (Tf) is largely unknown. The aim of the present study was to investigate the effects of glycation on the distribution of Fe3+ on the two Fe3+ -binding sites of Tf. METHODS: In vitro glycation of Tf was accomplished by preincubation with glucose for 14 days. Tf was loaded with Fe3+ compounds to achieve theoretical Tf Fe3+ saturations of 32%, 64%, and 96% (monitored by spectrophotometry). Fe3+ -Tf isoforms were separated by isoelectric focusing. RESULTS: Fe3+ binding was highest when Tf was incubated with Fe:nitrilotriacetic acid and reached a steady state overnight. Increasing the Fe3+ load led to a shift of isoform profile toward the diferric form (Fe2-Tf): in freshly prepared Tf, Fe2-Tf represented 6%, 30%, and 66% of all isoforms at 32%, 64%, and 96% theoretical Fe3+ saturation, respectively. Fe3+ was equally distributed to the monoferric Tf forms with Fe3+ bound to the amino (Fe1N-Tf) and carboxy termini (Fe1C-Tf). Glycation decreased binding of Fe3+ to Tf (monitored at 450 nm). At low theoretical Fe3+ saturation (32%), glycation increased the mean (SD) proportion of Fe2-Tf: 18 (3)% in the presence of 33.3 mmol/L glucose vs 12 (4)% with 0 mmol/L glucose (P = 0.01). In contrast, at 96% theoretical Fe3+ saturation, Fe2-Tf decreased linearly with increasing glycation (r = 0.97; P = 0.008). Preincubation, independent of glycation, favored the Fe1N-Tf isoform at 64% theoretical Fe3+ saturation [27 (0.7)% vs 23 (1.1)% of the Fe1C-Tf isoform; P = 0.009]. CONCLUSIONS: Glycation impairs Fe3+ binding and affects Fe3+ -Tf isoform distribution depending on concentration. The diagnostic implications of these results need further elucidation in clinical studies.

Ferric Compounds↗
PubMed2003

Essential metals--case study on iron.

Iron is a vital element in life. Because of the insolubility of iron oxides and sulfides the implication is that dissolved iron was fairly abundant and that oxygen and sulfide were rare in the atmosphere and ocean. Iron and its compounds present as pollutants in the atmosphere can cause deleterious effects to humans, animals, and materials. Analyses of urban air samples show that the iron content averages 1.6 microg/m(3), with the iron and steel industry probably the most likely source of emission. Iron is a natural component of soils and its concentration can be influenced by some industries. Iron concentration in surface water varies greatly, from 61 ppm to 2680 ppm. The disposition of iron in the human body is regulated by a complex mechanism to maintain homeostasis. Iron concentrations in body tissues must be tightly regulated because excessive iron leads to tissue damage, as a result of formation of free radicals. Iron has the capacity to accept and donate electrons readily. The content of body iron is regulated primarily by absorption since humans have no physiological mechanism by which excess iron is excreted. Iron has been identified as a component of asbestos and other mineral and synthetic fibers. Inhalation of iron oxide fumes or dust by workers in the metal industries may result in deposition of iron particles in lungs, producing an X-ray appearance resembling silicosis. During the last decades efforts regarding dietary iron supply focused mostly on the prevention of deficiencies, especially during growth and pregnancy. The chemical form of the iron influences absorption, as do interrelationships with other dietary components.

Absorption↗
PubMed1999

The application of ion chromatographic method for bioavailability and stability test of iron preparations.

Postabsorptive serum iron level was determined after oral administration of the compounds to human. In serum and whole blood, Fe3+ was measured by ion chromatography (IC) using a pyridine-2,6-dicarboxylic acid (PDCA) as an eluent. The serum sample solutions were pretreated with I N HCI and 50% TCA. The whole blood sample solutions were treated with 3 N HCI for 30 min at 125 degrees C. The limit of detection (LOD) of the IC technique is 0.2 microM for Fe2- and 0.1 microM for Fe3+. The area under concentration (AUC) can be obtained by the above analytical condition. In addition, to compare the stability of Fe2+ to that of Fe3+ in pharmaceutical preparations, accelerated stability test was carried out. After storing the samples under 40 degrees C, 75%RH in light-resistant container for various time intervals, the contents of iron of different valencies were determined separately by the IC technique and the change and/or the interchange of among those iron species in preparations was investigated. Iron raw materials are stable, but Fe2+ in Fe3+ source materials was slightly converted to Fe3+ by oxidation. Fe2+ in Fe3+ source raw materials and Fe3+ in Fe2+ raw materials are determined as impurities. Therefore, IC technique is found to be an appropriate method for comparative evaluation of dissimilar bioavailability of Fe2+ and Fe3+, stability of Fe2+ and Fe3+ raw materials and preparations.

Biological Availability↗
PubMed1994

Chloroquine induces human macrophage killing of Histoplasma capsulatum by limiting the availability of intracellular iron and is therapeutic in a murine model of histoplasmosis.

We investigated the role of intracellular iron on the capacity of Histoplasma capsulatum (Hc) yeasts to multiply within human macrophages (Mphi). Coculture of Hc-infected Mphi with the iron chelator deferoxamine suppressed the growth of yeasts in a concentration-dependent manner. The effect of deferoxamine was reversed by iron-saturated transferrin (holotransferrin) but not by iron-free transferrin (apotransferrin). Chloroquine, which prevents release of iron from transferrin by raising endocytic and lysosomal pH, induced human Mphi to kill Hc. The effect of chloroquine was reversed by iron nitriloacetate, an iron compound that is soluble at neutral to alkaline pH, but not by holotransferrin, which releases iron only in an acidic environment. Chloroquine (40-120 mg/kg) given intraperitoneally for 6 d to Hc-infected C57BL/6 mice significantly reduced the growth of Hc in a dose-dependent manner. At 120 mg/kg there was a 17- and 15-fold reduction (P < 0.01) in CFU in spleens and livers, respectively. The therapeutic effect of chloroquine also correlated with the length of treatment. As little as 2 d of chloroquine therapy (120 mg/kg), when started at day 5 after infection, reduced CFU in the spleen by 50%. Treatment with chloroquine for 10 d after a lethal inoculum of Hc protected six of nine mice; all control mice were dead by day 11 (P = 0.009). This study demonstrates that: (a) iron is of critical importance to the survival and multiplication of Hc yeasts in human Mphi; (b) in vitro, chloroquine induces Mphi killing of Hc yeasts by restricting the availability of intracellular iron; and (c) in vivo, chloroquine significantly reduces the number of organisms in the spleens and livers of Hc-infected mice and can protect mice from a lethal inoculum of Hc yeasts. Thus, chloroquine may be effective in the treatment of active histoplasmosis and also may be useful in preventing relapse of histoplasmosis in patients with acquired immunodeficiency syndromes.

Animals↗
PubMed2005

Nutritional and technological behavior of stabilized iron-gluconate in wheat flour.

Food fortification has been shown to be an effective strategy to overcome iron malnutrition. When a new iron compound is developed for this purpose, it must be evaluated from a nutritional and technological point of view before adding it into foods. In this way, we have evaluated ferrous gluconate stabilized by glycine as a new iron source to be used in wheat flour fortification. We performed biological studies in rats as well as sensory perceptions by human subjects in wheat flour fortified with this iron source. The productions of pentane as a rancidity indicator as well as the change of the sensorial properties of the biscuits made with stabilized ferrous gluconate-fortified wheat flour were negligible. Iron absorption in water from this iron source was similar to the reference standard ferrous sulfate. Nevertheless, because of the phytic acid content, iron absorption from fortified wheat flour decrease 40% for both iron sources. The addition of zinc from different sources did not modify iron absorption from ferrous sulfate and stabilized ferrous gluconate in water and wheat flour. The iron absorption mechanism as well as the biodistribution studies demonstrate that the biological behavior of this iron source does not differ significantly from the reference standard. These results demonstrate that the iron source under study has adequate properties to be used in wheat flour fortification. Nevertheless, more research is needed before considering this iron source for its massive use in food fortification.

Animals↗
PubMed1994

Role of methionine 230 in intramolecular electron transfer between the oxyferryl heme and tryptophan 191 in cytochrome c peroxidase compound II.

The kinetics of electron transfer from cytochrome c (CC) to yeast cytochrome c peroxidase (CcP) compound I were studied by flash photolysis and stopped-flow spectroscopy. Flash photolysis studies employed horse CC derivatives labeled at specific lysine amino groups with (dicarboxybipyridine)bis-(bipyridine)ruthenium (Ru-CC). Initial electron transfer from Ru-CC reduced the indole radical on Trp-191 of CcP compound I [CMPI(IV,R.)], producing CMPII(IV,R). This reaction was biphasic for each of several Ru-CC derivatives, with rate constants which varied according to the position of the Ru label. For Ru-27-CC labeled at lysine 27, rate constants of 43,000 and 1600 s-1 were observed at pH 5.0 in 2 mM acetate. After reduction of the indole radical by Ru-CC, intramolecular electron transfer from Trp-191 to the oxyferryl heme in CMPII(IV,R) was observed, producing CMPII(III,R.). The rate constant and extent of this intramolecular electron transfer reaction were independent of both the protein concentration and the Ru-CC derivative employed. The rate constant decreased from 1100 s-1 at pH 5 to 550 s-1 at pH 6, while the extent of conversion of CMPII(IV,R) to CMPII(III,R.) decreased from 56% at pH 5 to 29% at pH 6. The reaction was not detected at pH 7.0 and above. The pH dependence of the rate and extent of this internal electron transfer reaction paralleled the pH dependence of the rate of bimolecular reduction of CMPII(IV,R) by native horse CC measured by stopped-flow spectroscopy at high ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Isolation, properties and structural studies on a compound from tunicate blood cells that may be involved in vanadium accumulation.

A novel compound, for which the trivial name tunichrome is proposed, was isolated from the vanadium-rich blood cells of the tunicate Ascidia niga. Preliminary structural studies suggest a molecular weight of about 390, the presence of conjugated vinyl groups, and an acidic group, possibly carboxyl, with an apparent pKa of 3.0. Elements C, H, N and O comprise 98.4% of the sample weight, the number of atoms per mol of tunichrome being 14.1, 22.2, 1.5 and 10.6 respectively, which indicates some heterogeneity in the sample. Tunichrome readily reduces Fe(III) and V(V). In an initial fast step, 2 mol of V(V) are reduced, or 4 mol of Fe(III)-phenanthroline per mol of tunichrome; in a further slow reaction, another 9 mol of Fe(III)-phenanthroline or Fe(III)-bipyridine are reduced. The initial reaction is first-order with respect to tunichrome and Fe(III). Above pH 3.5, tunichrome is rapidly hydrolysed, 13 mol of OH- being consumed per mol of tunichrome. The hydrolysis involves polymerization and loss of the characteristic absorption peak at 325 nm. It is suggested that the presence of tunichrome may be linked to vanadium accumulation by the blood cells. The mechanism involves entry of vanadate via an anionic channel into vacuoles of the blood cells, where it is reduced to V(IV) or V(III), both of which, being cationic, cannot escape from the vacuole.

Animals↗
PubMed2003

Development of supported iron oxide catalyst for destruction of PCDD/F.

Studies on the development of supported iron oxide catalysts for PCDD/F decomposition using 2-monochlorophenol as a surrogate test compound are presented. Iron oxide catalysts supported on titania were prepared by two methods: impregnation and the sol-gel method. The latter preparation method resulted in better dispersion of iron oxide on the surface and the formation of gamma-Fe2O3. This is in contrast to the impregnated samples where alpha-Fe2O3 crystallites were formed. Formation of gamma-Fe2O3 resulted in improved reducibility of the active phase that favorably affected the catalytic oxidation properties of the catalyst, i.e., the light-off curves for the sol-gel samples were shifted toward lower temperature. Addition of calcium oxide to iron oxide catalyst further improved the performance of the system through stabilization and increase in the concentration of gamma-Fe2O3 in the sol-gel prepared samples. Addition of calcium oxide has a dual effect on the performance of the catalyst. First, it creates oxygen vacancies in the reduction-resistant Fe2O3 octahedral structures, thereby improving the reducibility of the active phase. Second, iron oxide can transform during decomposition of chlorinated hydrocarbons into iron chloride. Calcium oxide improved the chlorine transfer from the surface iron oxide species, thereby providing a relatively fresh surface for further catalytic oxidation. Comparison of TPR profiles with the position of light-off curves in 2-monochlorophenol decomposition led to the conclusion that Fe3O4 species are the active phase under conditions that facilitate redox cycling between Fe3+ and Fe2+ ions.

Benzofurans↗