Peroxidative activities of hemoglobin and hemoglobin derivatives

Capturing a bis-Fe(IV) State in Methylosinus trichosporium OB3b MbnH

The diheme bacterial cytochrome c peroxidase (bCcP)/MauG superfamily is a diverse set of enzymes that remains largely uncharacterized. One recently discovered member, MbnH, converts a tryptophan residue in its substrate protein, MbnP, to kynurenine. Here we show that upon reaction with H₂O₂, MbnH forms a bis-Fe(IV) intermediate, a state previously detected in just two other enzymes, MauG and BthA. Using absorption, Mössbauer, and electron paramagnetic resonance (EPR) spectroscopies coupled with kinetic analysis, we characterized the bis-Fe(IV) state of MbnH and determined that this intermediate decays back to the diferric state in the absence of MbnP substrate. In the absence of MbnP substrate, MbnH can also detoxify H₂O₂ to prevent oxidative self damage, unlike MauG, which has long been viewed as the prototype for bis-Fe(IV) forming enzymes. MbnH performs a different reaction from MauG, while the role of BthA remains unclear. All three enzymes can form a bis-Fe(IV) intermediate but within distinct kinetic regimes. The study of MbnH significantly expands our knowledge of enzymes that form this species. Computational and structural analyses indicate that electron transfer between the two heme groups in MbnH and between MbnH and the target tryptophan in MbnP likely occurs via a hole-hopping mechanism involving intervening tryptophan residues. These findings set the stage for discovery of additional functional and mechanistic diversity within the bCcP/MauG superfamily.

Distribution of microglia/immune cells in the brain of adult zebrafish in homeostatic and regenerative conditions: Focus on oxidative stress during brain repair

Microglia are macrophage-like cells exerting determinant roles in neuroinflammatory and oxidative stress processes during brain regeneration. We used zebrafish as a model of brain plasticity and repair. First, by performing L-plastin (Lcp1) immunohistochemistry and using transgenic Tg(mpeg1.1:GFP) or Tg(mpeg1.1:mCherry) fish, we analyzed the distribution of microglia/immune cells in the whole brain. Specific regional differences were evidenced in terms of microglia/immune cell density and morphology (elongated, branched, highly branched, and amoeboid). Taking advantage of Tg(fli:GFP) and Tg(GFAP::GFP) enabling the detection of endothelial cells and neural stem cells (NSCs), we highlighted the association of elongated microglia/immune cells with blood vessels and rounded/amoeboid microglia with NSCs. Second, after telencephalic injury, we showed that L-plastin cells were still abundantly present at 5 days post-lesion (dpl) and were associated with regenerative neurogenesis. Finally, RNA-sequencing analysis from injured telencephalon (5 dpl) confirmed the upregulation of microglia/immune cell markers and highlighted a significant increase of genes involved in oxidative stress (nox2, nrf2a, and gsr). The analysis of antioxidant activities at 5 dpl also revealed an upregulation of superoxide dismutase and persistent H₂ O₂ generation in the injured telencephalon. Also, microglia/immune cells were shown to be a source of oxidative stress at 5 dpl. Overall, our data provide a better characterization of microglia/immune cell distribution in the healthy zebrafish brain, highlighting some evolutionarily conserved features with mammals. They also emphasize that 5 days after injury, microglia/immune cells are still activated and are associated to a persistent redox imbalance. Together, these data raise the question of the role of oxidative stress in regenerative neurogenesis in zebrafish.

Oxidative Implications of Substituting a Conserved Cysteine Residue in Sugar Beet Phytoglobin BvPgb 1.2

Phytoglobins (Pgbs) are plant-originating heme proteins of the globin superfamily with varying degrees of hexacoordination. Pgbs have a conserved cysteine residue, the role of which is poorly understood. In this paper, we investigated the functional and structural role of cysteine in BvPgb1.2, a Class 1 Pgb from sugar beet (Beta vulgaris), by constructing an alanine-substituted mutant (Cys86Ala). The substitution had little impact on structure, dimerization, and heme loss as determined by X-ray crystallography, size-exclusion chromatography, and an apomyoglobin-based heme-loss assay, respectively. The substitution significantly affected other important biochemical properties. The autoxidation rate increased 16.7- and 14.4-fold for the mutant versus the native protein at 25 °C and 37 °C, respectively. Thermal stability similarly increased for the mutant by ~2.5 °C as measured by nano-differential scanning fluorimetry. Monitoring peroxidase activity over 7 days showed a 60% activity decrease in the native protein, from 33.7 to 20.2 U/mg protein. When comparing the two proteins, the mutant displayed a remarkable enzymatic stability as activity remained relatively constant throughout, albeit at a lower level, ~12 U/mg protein. This suggests that cysteine plays an important role in BvPgb1.2 function and stability, despite having seemingly little effect on its tertiary and quaternary structure.

Ergothioneine: A Stress Vitamin with Antiaging, Vascular, and Neuroprotective Roles?

Significance: Ergothioneine (ET) is an unusual sulfur-containing amino acid derived from histidine, acquired predominantly from food. Its depletion is associated with deleterious consequences in response to stress stimuli in cell culture models, prompting us to classify it as a vitamin in 2010, which was later supported by in vivo studies. ET is obtained from a variety of foods and is taken up by a selective transporter. ET possesses antioxidant and anti-inflammatory properties that confer cytoprotection. ET crosses the blood-brain barrier and has been reported to have beneficial effects in the brain. In this study, we discuss the cytoprotective and neuroprotective properties of ET, which may be harnessed for combating neurodegeneration and decline during aging. Recent Advances: The designation of ET as a stress vitamin is gaining momentum, opening a new field of investigation involving small molecules that are essential for optimal physiological functioning and maintenance of health span. Critical Issues: Although ET was discovered more than a century ago, its physiological functions are still being elucidated, especially in the brain. As ET is present in most foods, toxicity associated with its deprivation has been difficult to assess. Future Directions: Using genetically engineered cells and mice, it may now be possible to elucidate roles of ET. This coupled with advances in genomics and metabolomics may lead to identification of ET function. As ET is a stable antioxidant with anti-inflammatory properties, whose levels decline during aging, supplementing ET in the diet or consuming an ET-rich diet may prove beneficial. Antioxid. Redox Signal. 36, 1306-1317.

Oxidative degradation perturbs physico-chemical properties of hemoglobin in cigarette smokers: a threat to different biomolecules

CONTEXT

Cigarette smokers develop structural modification in hemoglobin (Hb) and this modification enable Hb to undergo higher rate of auto-oxidation, leading to generation of further intracellular ROS.

OBJECTIVE

In this study, we exhibited the possible cause and consequences of Hb modification in cigarette smokers.

METHODS

Twenty-two smokers and 16 nonsmokers, aged 25 to 35 years, having a smoking history of 7-10 years were recruited in this study. Carbonyl content, ferryl form, peroxidase-like and esterase-like activities of Hb were assayed. Free iron release by Hb, erythrocyte membrane-bound Hb and plasma Hb were also measured along with assessment of important biomolecular degradations by Hb.

RESULTS AND DISCUSSION

Increase in carbonyl content in Hb indicates its oxidative degradation. Increase in ferryl Hb formation, peroxidase-like activity and decrease in esterase like activity of Hb along with increased release of nonheme iron (from Hb) clearly indicates alteration in physico-chemical properties of Hb in smokers. Moreover, increase in erythrocyte membrane-bound Hb and plasma-free Hb provide further evidences for higher rate of Hb oxidation in smokers' erythrocyte. The rates of protein, lipid, sugar and DNA degradation were noticed to be higher by smokers' Hb; and were further attenuated by desferrioxamine as well as mannitol.

CONCLUSION

We conclude that in cigarette smokers, there is oxidative degradation of Hb and the degradation causes alteration in its physico-chemical properties, which in turn may degrade different biomolecules in its close vicinity by releasing more iron and production of more superoxide as well as hydroxyl radical.

Integrated Assessment of Nickel Electroplating Industrial Wastewater Effluent as a Renewable Resource of Irrigation Water Using a Hydroponic Cultivation System

Nickel, a micronutrient essential for plant growth and development, has been recognized as a metallic pollutant in wastewater. The concentration of nickel ions in the water course, exceeding the maximum tolerable limit, has called for an alarming attention, due to the bioaccumulative entry in the water-plant-human food chain, leaving a burden of deteriorative effects on visible characteristics, physiological processes, and oxidative stress response in plants. In this work, the renewable utilization of nickel electroplating industrial wastewater effluent (0, 5, 10, 25, 50, and 100%) as a viable source of irrigation water was evaluated using a hydroponic cultivation system, by adopting Lablab purpureus and Brassica chinensis as the plant models, in relation to the physical growth, physiological and morphological characteristics, photosynthetic pigments, proline, and oxidative responses. The elongation of roots and shoots in L. purpureus and B. chinensis was significantly inhibited beyond 25 and 5% of industrial wastewater. The chlorophyll-a, chlorophyll-b, total chlorophyll, and carotenoid contents, accompanied by alterations in the morphologies of xylem, phloem, and distortion of stomata, were recorded in the industrial wastewater-irrigated groups, with pronounced toxicity effects detected in B. chinensis. Excessive proline accumulation was recorded in the treated plant models. Ascorbate peroxidase (APX), guaiacol peroxidase (POD), and catalase (CAT) scavenging activities were drastically altered, with a profound upregulation effect in the POD activity in L. purpureus and both POD and APX in B. chinensis, predicting the nickel-induced oxidative stress. Conclusively, the diluted industrial wastewater effluent up to the optimum concentrations of 5 and 25%, respectively, could be feasibly reused as a renewable resource for B. chinensis and L. purpureus irrigation, verified by the minimal or negligible phytotoxic implications in the plant models. The current findings have shed light on the interruption of nickel-contaminated industrial wastewater effluent irrigation practice on the physical and biochemical features of food crops and highlighted the possibility of nutrient recycling via wastewater reuse in a sustainable soilless cultivation.

Non enzymatic covalent modification by glycolysis end product converts hemoglobin into its oxidative stress potency state

The effect of glycation by Pyruvic acid (PA) on the early and advanced conformational changes in Hemoglobin (Hb) was studied. Multi Spectroscopic measurement revealed that Hb undergoes structural conformational changes and unbound heme upon incubation with PA. These covalent modifications were followed by the reduction of heme centre and these reduction processes initiates its peroxidase-like activity. An extended PA glycation resulted in the appearance of advanced glycation end products fluorescence, with notable changes in compositions of secondary structure. The amyloidogenic state was confirmed by SEM, fluorescence microscope observation. This study reveals an insight to the role of pyruvic acid which increases the oxidative stress due to the heme reduction and diabetic complication.

Impaired brain homeostasis and neurogenesis in diet-induced overweight zebrafish: a preventive role from A. borbonica extract

Overweight and obesity are worldwide health concerns leading to many physiological disorders. Recent data highlighted their deleterious effects on brain homeostasis and plasticity, but the mechanisms underlying such disruptions are still not well understood. In this study, we developed and characterized a fast and reliable diet-induced overweight (DIO) model in zebrafish, for (1) studying the effects of overfeeding on brain homeostasis and for (2) testing different preventive and/or therapeutic strategies. By overfeeding zebrafish for 4 weeks, we report the disruption of many metabolic parameters reproducing human overweight features including increased body weight, body mass index, fasting blood glucose levels and liver steatosis. Furthermore, DIO fish displayed blood–brain barrier leakage, cerebral oxidative stress, neuroinflammation and decreased neurogenesis. Finally, we investigated the preventive beneficial effects of A. borbonica, an endogenous plant from Reunion Island. Overnight treatment with A. borbonica aqueous extract during the 4 weeks of overfeeding limited some detrimental central effects of DIO. In conclusion, we established a relevant DIO model in zebrafish demonstrating that overfeeding impairs peripheral and central homeostasis. This work also highlights the preventive protective effects of A. borbonica aqueous extracts in DIO, and opens a way to easily screen drugs aiming at limiting overweight and associated neurological disorders.

Enhanced oxidative stress and damage in glycated erythrocytes

Diabetes is associated with a dramatic mortality rate due to its vascular complications. Chronic hyperglycemia in diabetes leads to enhanced glycation of erythrocytes and oxidative stress. Even though erythrocytes play a determining role in vascular complications, very little is known about how erythrocyte structure and functionality can be affected by glycation. Our objective was to decipher the impact of glycation on erythrocyte structure, oxidative stress parameters and capacity to interact with cultured human endothelial cells. In vitro glycated erythrocytes were prepared following incubation in the presence of different concentrations of glucose. To get insight into the in vivo relevance of our results, we compared these data to those obtained using red blood cells purified from diabetics or non-diabetics. We measured erythrocyte deformability, susceptibility to hemolysis, reactive oxygen species production and oxidative damage accumulation. Altered structures, redox status and oxidative modifications were increased in glycated erythrocytes. These modifications were associated with reduced antioxidant defence mediated by enzymatic activity. Enhanced erythrocyte phagocytosis by endothelial cells was observed when cultured with glycated erythrocytes, which was associated with increased levels of phosphatidylserine-likely as a result of an eryptosis phenomenon triggered by the hyperglycemic treatment. Most types of oxidative damage identified in in vitro glycated erythrocytes were also observed in red blood cells isolated from diabetics. These results bring new insights into the impact of glycation on erythrocyte structure, oxidative damage and their capacity to interact with endothelial cells, with a possible relevance to diabetes.

Bioanalytical Application of Peroxidase-Mimicking DNAzymes: Status and Challenges

DNAzymes with peroxidase-mimicking activity are a new class of catalytically active DNA molecules. This system is formed as a complex of hemin and a G-quadruplex structure created by oligonucleotides rich in guanine. Considering catalytic activity, this DNAzyme mimics horseradish peroxidase, the enzyme most commonly used for signal generation in bioassays. Because DNAzymes exhibit many advantages over protein enzymes (thermal stability, easy and cheap synthesis and purification) they can successfully replace HRP in bioanalytical applications. HRP-like DNAzymes have been applied in the detection of several DNA sequences. Many amplification techniques have been conjugated with DNAzyme systems, resulting in ultrasensitive bioassays. On the other hand, the combination of aptamers and DNAzymes has led to the development of aptazymes for specific targets. An up-to-date summary of the most interesting DNAzyme-based assays is presented here. The elaborated systems can be used in medical diagnosis or chemical and biological studies.

Gamma irradiation protect the developing wheat endosperm from oxidative damage by balancing the trade-off between the defence network and grains quality

Gamma irradiation has been reported to modulate the biochemical and molecular parameters associated with the tolerance of plant species under biotic/ abiotic stress. Wheat is highly sensitive to heat stress (HS), as evident from the decrease in the quantity and quality of the total grains. Here, we studied the effect of pre-treatment of wheat dry seeds with different doses of gamma irradiation (0.20, 0.25 and 0.30 kGy) on tolerance level and quality of developing wheat endospermic tissue under HS (38 °C, 1 h; continuously for three days). Expression analysis of genes associated with defence and starch metabolism in developing grains showed maximum transcripts of HSP17 (in response to 0.25 kGy + HS) and AGPase (under 0.30 kGy), as compared to control. Gamma irradiation was observed to balance the accumulation of H₂O₂ by enhancing the activities of SOD and GPx in both the cvs. under HS. Gamma irradiation was observed to stabilize the synthesis of starch and amylose by regulating the activities of AGPase, SSS and α-amylase under HS. The appearance of isoforms of gliadins (α, β, γ, ω) were observed more in gamma irradiated seeds (0.20 kGy), as compared to control. Gamma irradiation (0.25 kGy in HD3118 & 0.20 kGy in HD3086) was observed to have positive effect on the width, length and test seed weight of the grains under HS. The information generated in present investigation provides easy, cheap and user-friendly technology to mitigate the effect of terminal HS on the grain-development process of wheat along with development of robust seeds with high nutrient density.

Ergothioneine stands out from hercynine in the reaction with singlet oxygen: Resistance to glutathione and TRIS in the generation of specific products indicates high reactivity

The candidate vitamin ergothioneine (ET), an imidazole-2-thione derivative of histidine betaine, is generally considered an antioxidant. However, the precise physiological role of ET is still unresolved. Here, we investigated in vitro the hypothesis that ET serves specifically to eradicate noxious singlet oxygen (¹O₂). Pure ¹O₂ was generated by thermolysis at 37°C of N,N'-di(2,3-dihydroxypropyl)-1,4-naphthalenedipropanamide 1,4-endoperoxide (DHPNO₂). Assays of DHPNO₂ with ET or hercynine (= ET minus sulfur) at pH 7.4 were analyzed by LC-MS in full scan mode to detect products. Based on accurate mass and product ion scan data, several products were identified and then quantitated as a function of time by selected reaction monitoring. All products of hercynine contained, after a [4+2] cycloaddition of ¹O₂, a carbonyl at position 2 of the imidazole ring. By contrast, because of the doubly bonded sulfur, we infer from the products of ET as the initial intermediates a 4,5-dioxetane (after [2+2] cycloaddition) and hydroperoxides at position 4 and 5 (after Schenck ene reactions). The generation of single products from ET, but not from hercynine, was fully resistant to a large excess of tris(hydroxymethyl)aminomethane (TRIS) or glutathione (GSH). This suggests that ¹O₂ markedly favors ET over GSH (at least 50-fold) and TRIS (at least 250-fold) for the initial reaction. Loss of ET was almost abolished in 5mM GSH, but not in 25mM TRIS. Regeneration of ET seems feasible, since some ET products - by contrast to hercynine products - decomposed easily in the MS collision cell to become aromatic again.

Peroxidase activity and involvement in the oxidative stress response of roseobacter denitrificans truncated hemoglobin

Roseobacter denitrificans is a member of the widespread marine Roseobacter genus. We report the first characterization of a truncated hemoglobin from R. denitrificans (Rd. trHb) that was purified in the heme-bound form from heterologous expression of the protein in Escherichia coli. Rd. trHb exhibits predominantly alpha-helical secondary structure and absorbs light at 412, 538 and 572 nm. The phylogenetic classification suggests that Rd. trHb falls into group II trHbs, whereas sequence alignments indicate that it shares certain important heme pocket residues with group I trHbs in addition to those of group II trHbs. The resonance Raman spectra indicate that the isolated Rd. trHb contains a ferric heme that is mostly 6-coordinate low-spin and that the heme of the ferrous form displays a mixture of 5- and 6-coordinate states. Two Fe-His stretching modes were detected, notably one at 248 cm^-1, which has been reported in peroxidases and some flavohemoglobins that contain an Fe-His-Asp (or Glu) catalytic triad, but was never reported before in a trHb. We show that Rd. trHb exhibits a significant peroxidase activity with a (k_cat/K_m) value three orders of magnitude higher than that of bovine Hb and only one order lower than that of horseradish peroxidase. This enzymatic activity is pH-dependent with a pK_a value ~6.8. Homology modeling suggests that residues known to be important for interactions with heme-bound ligands in group II trHbs from Mycobacterium tuberculosis and Bacillus subtilis are pointing toward to heme in Rd. trHb. Genomic organization and gene expression profiles imply possible functions for detoxification of reactive oxygen and nitrogen species in vivo. Altogether, Rd. trHb exhibits some distinctive features and appears equipped to help the bacterium to cope with reactive oxygen/nitrogen species and/or to operate redox biochemistry.

Comparative study on thiol drugs' effect on tert-butyl hydroperoxide induced luminol chemiluminescence in human erythrocyte lysate and hemoglobin oxidation

The current studies have investigated the effect of heterocyclic drugs with the single thiol group (thiamazole, mercaptopurine) and dithiol aliphatic drugs (dimercaptosuccinic acid, dithiothreitol) under oxidative stress conditions, using tert-butyl hydroperoxide (t-BuOOH), in human erythrocyte lysate with the luminol-enhanced chemiluminescence technique. Knowing that oxidative processes induced by t-BuOOH are triggered by (oxy)hemoglobin (Hb), the effect of different thiol drugs (RSH) on isolated human Hb oxidation to methemoglobin (MHb) and hemichromes (HChr) was further considered. Three types of chemiluminescence curves, fitting to logistic-exponential model, have been revealed under influence of RSH. Structure of the data (MHb and HChr production, and free radical activity of RSH) in Principal Component Analysis visualization and kinetic profiles of chemiluminescence integrate information in terms of the diversity of RSH reaction mechanisms depending on the specific molecular context of the given thiol: aliphatic or aromatic nature as well as the number and position of the -SH groups in the molecule. The study conducted in presented in vitro systems indicates the potential role of thiol drugs mediated toxicity in an oxidative stress dependent mechanism.

Deferiprone: structural and functional modulating agent of hemoglobin fructation

Diabetic complication arises from the presence of advanced glycation end products in different sites of the body. Great attention should be paid to recognizing anti-glycation compounds. Here, deferiprone as an oral iron chelator drug administrated in treatment of β-thalassemic patients was selected to find its effect on the fructation of hemoglobin (Hb). Our results indicated that deferiprone could prevent the AGE and carbonyl formation via inhibition of structural changes in the structure of Hb during the fructation process. Moreover, deferiprone can preserve peroxidase and esterase activities of fructated Hb similar to native Hb. Therefore, deferiprone can be introduced as an anti-glycation drug to prevent the AGE formation.

High temperature unfolding of a truncated hemoglobin by molecular dynamics simulation

Heme containing proteins are associated with peroxidase activity. The proteins like hemoglobin, myoglobins, cytochrome c and micro-peroxidase other than peroxidases have been shown to exhibit weak peroxidase-like activity. This weak peroxidase-like activity in hemoglobin-like molecules is due to heme moiety. We conducted molecular dynamics (MD) studies to decipher the unfolding path of Ba-Glb (a truncated hemoglobin from Bacillus anthracis) and the role of heme moiety to its unfolding path. The similar unfolding path is also observed in vitro by UV/VIS spectroscopy. The data confirmed that the unfolding of Ba-Glb follows a three state process with a meta-stable (intermediate) state between the native and unfolded conformations. The present study is supported by several unfolding parameters like root-mean-square-deviation (RMSD), dictionary of protein secondary structure (DSSP), and free energy landscape. Understanding the structure of hemoglobin like proteins in unicellular dreaded pathogens like B. anthracis will pave way for newer drug discovery targets and in the disease management of anthrax.

Desferal as improving agent for hemoglobin fructation: structural and functional impacts

Hyperglycemia and advanced glycation end products (AGEs) have considerable effects in diabetic patients. So, the recognition of anti-glycation property of compounds has a substantial benefit. Here, desferal, an iron chelator which is one of the most effective drugs in β-thalassemia patients, was chosen to explore its effects on the fructation process of hemoglobin (Hb). The results indicated that desferal had a retardation effect on the functional and structural changes of Hb during fructation. It can prevent the AGE and carbonyl formations and helix depletion during the Hb fructation process. Moreover, desferal can preserve peroxidase and esterase activities of fructated Hb similar as native Hb. Therefore, desferal can be introduced as an anti-glycation drug to prevent the AGE formation.

Methylglyoxal-induced modifications of hemoglobin: structural and functional characteristics

Methylglyoxal (MG) reacts with proteins to form advanced glycation end products (AGEs). Although hemoglobin modification by MG is known, the modified protein is not yet characterized. We have studied the nature of AGE formed by MG on human hemoglobin (HbA(0)) and its effect on structure and function of the protein. After reaction of HbA(0) with MG, the modified protein (MG-Hb) was separated and its properties were compared with those of the unmodified protein HbA(0). As shown by MALDI-mass spectrometry, MG converted Arg-92α and Arg-104β to hydroimidazolones in MG-Hb. Compared to HbA(0), MG-Hb exhibited decreased absorbance around 280nm, reduced tryptophan fluorescence (excitation 285nm) and increased α-helix content. However, MG modification did not change the quaternary structure of the heme protein. MG-Hb appeared to be more thermolabile than HbA(0). The modified protein was found to be more effective than HbA(0) in H(2)O(2)-mediated iron release and oxidative damages involving Fenton reaction. MG-Hb exhibited less peroxidase activity and more esterase activity than HbA(0). MG-induced structural and functional changes of hemoglobin may enhance oxidative stress and associated complications, particularly in diabetes mellitus with increased level of MG.

Oxidation of thiamine on reaction with nitrogen dioxide generated by ferric myoglobin and hemoglobin in the presence of nitrite and hydrogen peroxide

It is shown that nitrogen dioxide oxidizes thiamine to thiamine disulfide, thiochrome, and oxodihydrothiochrome (ODTch). The latter is formed during oxidation of thiochrome by nitrogen dioxide. Nitrogen dioxide was produced by incubation of nitrite with horse ferric myoglobin and human hemoglobin in the presence of hydrogen peroxide. After addition of tyrosine or phenol to aqueous solutions containing oxoferryl forms of the hemoproteins, thiamine, and nitrite, the yield of thiochrome greatly increased, whereas the yield of ODTch decreased. In the presence of high concentrations of tyrosine or phenol compounds ODTch was not formed at all. The neutral form of thiamine with the closed thiazole cycle and minor tricyclic form of thiamine do not enter the heme pocket of the protein and do not interact with the oxoferryl heme complex Fe(IV=O) or porphyrin radical. The tricyclic form of thiamine is oxidized to thiochrome by tyrosyl radicals located on the surface of the hemoprotein. The thiol form of thiamine is oxidized to thiamine disulfide by both hemoprotein tyrosyl radicals and oxoferryl heme complexes. Nitrite and also tyrosine, tyramine, and phenol readily penetrate into the heme pocket of the protein and reduce the oxyferryl complex to ferric cation. These reactions yield nitrogen dioxide as well as tyrosyl and phenoxyl radicals of tyrosine molecules and phenol compounds, respectively. Tyrosyl and phenoxyl radicals of low molecular weight compounds oxidize thiamine only to thiochrome and thiamine disulfide. The effect of oxoferryl forms of myoglobin and hemoglobin, nitrogen dioxide, and phenol on thiamine oxidative transformation as well as antioxidant properties of the hydrophobic thiamine metabolites thiochrome and ODTch are discussed.

Characterization of G-quadruplex/hemin peroxidase: substrate specificity and inactivation kinetics

Recently, G-quadruplex/hemin (G4/hemin) complexes have been found to exhibit peroxidase activity, and this feature has been extensively exploited for colorimetric detection of various targets. To further understand and characterize this important DNAzyme, its substrate specificity, inactivation mechanism, and kinetics have been examined by comparison with horseradish peroxidase (HRP). G4/hemin DNAzyme exhibits broader substrate specificity and much higher inactivation rate than HRP because of the exposure of the catalytic hemin center. The inactivation of G4/hemin DNAzyme is mainly attributed to the degradation of hemin by H(2)O(2) rather than the destruction of G4. Both the inactivation rate and catalytic oxidation rate of G4/hemin DNAzyme depend on the concentration of H(2)O(2), which suggests that active intermediates formed by G4/hemin and H(2)O(2) are the branch point of catalysis and inactivation. Reducing substrates greatly inhibit the inactivation of G4/hemin DNAzyme by rapidly reacting with the active intermediates. A possible catalytic and inactivation process of G4/hemin has been proposed. These results imply a potential cause for the hemin-mediated cellular injury and provide insightful information for the future application of G4/hemin DNAzyme.

Covalent modifications of hemoglobin by nitrite anion: formation kinetics and properties of nitrihemoglobin

The green nitrihemoglobin (α(2)β(2) tetramer, NHb) was prepared by the aerobic reaction of excess nitrite with human hemoglobin A(0) under mildly acidic conditions. A rate equation was determined and found to depend on nitrite, hydrogen ion, and oxygen concentrations: -d[HbNO(2)]/dt = [k(1) + k(2)(K(a)[HNO(2)])[O(2)](1/2)][HbNO(2)], where k(1) = (2.4 ± 0.9) × 10(-4) s(-1), k(2) = (1 ± 0.2) × 10(5) M(-5/2) s(-1), and K(a) is the acid dissociation constant for nitrous acid (4.5 × 10(-4) M). Also, the chemical properties of NHb are compared to those of the normal hemoglobin (including the addition products of common oxidation states with exogenous ligands, the alkaline transitions of the ferric forms, and the oxygen binding characteristics of the ferrous forms) and were found to be nearly indistinguishable. Therefore, the replacement of a single vinyl hydrogen with a nitro group on the periphery of each macrocycle in hemoglobin does not significantly perturb the interaction between the hemes and the heme pockets. Because nonphotochemical reaction chemistry must necessarily be most dependent on electronic ground states, it follows that the clearly visible difference in color between hemoglobin A(0) and NHb must be associated primarily with the respective electronic excited states. The possibility of NHb formation in vivo and its likely consequences are considered.

Peroxidase activity of hemoglobin-haptoglobin complexes: covalent aggregation and oxidative stress in plasma and macrophages

As a hemoprotein, hemoglobin (Hb) can, in the presence of H(2)O(2), act as a peroxidase. In red blood cells, this activity is regulated by the reducing environment. For stroma-free Hb this regulation is lost, and the potential for Hb to become a peroxidase is high and further increased by inflammatory cells generating superoxide. The latter can be converted into H(2)O(2) and feed Hb peroxidase activity. Haptoglobins (Hp) bind with extracellular Hb and reportedly weaken Hb peroxidase activity. Here we demonstrate that: (i) Hb peroxidase activity is retained upon binding with Hp; (ii) in the presence of H(2)O(2), Hb-Hp peroxidase complexes undergo covalent cross-linking; (iii) peroxidase activity of Hb-Hp complexes and aggregates consumes reductants such as ascorbate and nitric oxide; (iv) cross-linked Hb-Hp aggregates are taken up by macrophages at rates exceeding those for noncovalently cross-linked Hb-Hp complexes; (v) the engulfed Hb-Hp aggregates activate superoxide production and induce intracellular oxidative stress (deplete endogenous glutathione and stimulate lipid peroxidation); (vi) Hb-Hp aggregates cause cytotoxicity to macrophages; and (vii) Hb-Hp aggregates are present in septic plasma. Overall, our data suggest that under conditions of severe inflammation and oxidative stress, peroxidase activity of Hb-Hp covalent aggregates may cause macrophage dysfunction and microvascular vasoconstriction, which are commonly seen in severe sepsis and hemolytic diseases.

Correlation between hemichrome stability and the root effect in tetrameric hemoglobins

Oxidation of Hbs leads to the formation of different forms of Fe(III) that are relevant to a range of biochemical and physiological functions. Here we report a combined EPR/x-ray crystallography study performed at acidic pH on six ferric tetrameric Hbs. Five of the Hbs were isolated from the high-Antarctic notothenioid fishes Trematomus bernacchii, Trematomus newnesi, and Gymnodraco acuticeps, and one was isolated from the sub-Antarctic notothenioid Cottoperca gobio. Our EPR analysis reveals that 1), in all of these Hbs, at acidic pH the aquomet form and two hemichromes coexist; and 2), only in the three Hbs that exhibit the Root effect is a significant amount of the pentacoordinate (5C) high-spin Fe(III) form found. The crystal structure at acidic pH of the ferric form of the Root-effect Hb from T. bernacchii is also reported at 1.7 A resolution. This structure reveals a 5C state of the heme iron for both the alpha- and beta-chains within a T quaternary structure. Altogether, the spectroscopic and crystallographic results indicate that the Root effect and hemichrome stability at acidic pH are correlated in tetrameric Hbs. Furthermore, Antarctic fish Hbs exhibit higher peroxidase activity than mammalian and temperate fish Hbs, suggesting that a partial hemichrome state in tetrameric Hbs, unlike in monomeric Hbs, does not remove the need for protection from peroxide attack, in contrast to previous results from monomeric Hbs.

In VitroNonenzymatic Glycation Enhances the Role of Myoglobin as a Source of Oxidative Stress

Metmyoglobin (Mb) was glycated by glucose in a non-enzymatic in vitro reaction. Amount of iron release from the heme pocket of myoglobin was found to be directly related with the extent of glycation. After in vitro glycation, the unchanged Mb and glycated myoglobin (GMb) were separated by ion exchange (BioRex 70) chromatography, which eliminated free iron from the protein fractions. Separated fractions of Mb and GMb were converted to their oxy forms -MbO2 and GMbO2, respectively. H2O2-induced iron release was significantly higher from GMbO2 than that from MbO2. This free iron, acting as a Fenton reagent, might produce free radicals and degrade different cell constituents. To verify this possibility, degradation of different cell constituents catalyzed by these fractions in the presence of H2O2 was studied. GMbO2 degraded arachidonic acid, deoxyribose and plasmid DNA more efficiently than MbO2. Arachidonic acid peroxidation and deoxyribose degradation were significantly inhibited by desferrioxamine (DFO), mannitol and catalase. However, besides free iron-mediated free radical reactions, role of iron of higher oxidation states, formed during interaction of H2O2 with myoglobin might also be involved in oxidative degradation processes. Formation of carbonyl content, an index of oxidative stress, was higher by GMbO2. Compared to MbO2, GMbO2 was rapidly autooxidized and co-oxidized with nitroblue tetrazolium, indicating increased rate of Mb and superoxide radical formation in GMbO2. GMb exhibited more peroxidase activity than Mb, which was positively correlated with ferrylmyoglobin formation in the presence of H2O2. These findings correlate glycation-induced modification of myoglobin and a mechanism of increased formation of free radicals. Although myoglobin glycation is not significant within muscle cells, free myoglobin in circulation, if becomes glycated, may pose a serious threat by eliciting oxidative stress, particularly in diabetic patients.

Fructose-induced structural and functional modifications of hemoglobin: implication for oxidative stress in diabetes mellitus

Increased fructose concentration in diabetes mellitus causes fructation of several proteins. Here we have studied fructose-induced modifications of hemoglobin. We have demonstrated structural changes in fructose-modified hemoglobin (Fr-Hb) by enhanced fluorescence emission with excitation at 285 nm, more surface accessible tryptophan residues by using acrylamide, changes in secondary and tertiary structures by CD spectroscopy, and increased thermolability by using differential scanning calorimetry in comparison with those of normal hemoglobin, HbA(0). Release of iron from hemoglobin is directly related with the extent of fructation. H2O2-induced iron release from Fr-Hb is significantly higher than that from HbA(0). In the presence of H2O2, Fr-Hb degrades arachidonic acid, deoxyribose and plasmid DNA more efficiently than HbA(0), and these processes are significantly inhibited by desferrioxamine or mannitol. Thus increased iron release from Fr-Hb may cause enhanced formation of free radicals and oxidative stress in diabetes. Compared to HbA(0), Fr-Hb exhibits increased carbonyl formation, an index of oxidative modification. Functional modification in Fr-Hb has also been demonstrated by its decreased peroxidase activity and increased esterase activity in comparison with respective HbA(0) activities. Molecular modeling study reveals Lys 7alpha, Lys 127alpha and Lys 66beta to be the probable potential targets for fructation in HbA(0).

Effect of non-enzymatic glycation on esterase activities of hemoglobin and myoglobin

Heme proteins--hemoglobin and myoglobin possess esterase activities. Studies with purified hemoglobin from normal individuals and diabetic patients revealed that the esterase activity as measured from hydrolysis of p-nitrophenyl acetate (p-NPA) was higher in diabetic condition and increased progressively with extent of the disease. HbA(1c), the major glycated hemoglobin, which increases proportionately with blood glucose level in diabetes mellitus, exhibited more esterase activity than the non-glycated hemoglobin fraction, HbA(0), as demonstrated spectrophotometrically as well as by activity staining. Glycation influenced esterase activity of hemoglobin by increasing the affinity for the substrate and the rate of the reaction. Both HbA(0) and HbA(1c)-mediated catalysis of p-NPA hydrolysis was pH-dependent. Esterase activity of in vitro-glycated myoglobin (GMb) was also higher than that of its non-glycated analog (Mb). The amplified esterase activities of hemoglobin and myoglobin might be associated with glycation-induced structural modifications of the proteins.

An investigation of the peroxidase activity of Vitreoscilla hemoglobin

In order to investigate the ability of the Vitreoscilla hemoglobin (VHb) to act as a peroxidase, the protein was overexpressed in Escerichia coli and purified using a 6xHis-tag. The peroxidase activity of VHb was studied using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferrocene carboxylic acid (FcCOOH) dopamine and L-dopa as substrates. The effects of external agents such as pH, salt concentration/ionic strength, and the thermal stability of VHb on the catalytic activity were assessed. The optimum pH for VHb using ABTS as a substrate was estimated to be 6-7. The VHb protein proved to be stable up to 80 degrees C, as judged by its peroxidase activity. Furthermore, NaCl concentrations up to 100 mM did not exert any significant effect on the activity. The catalytic activity against ABTS and FcCOOH was similar to that measured for horseradish peroxidase, whereas in the case of the phenolic substrates dopamine and L-dopa the activity was several orders of magnitude lower. The Michaelis constants, KmH2O2, were in good agreement with the data for human and bovine hemoglobin. No activity could be detected for the negative controls lacking VHb. These results demonstrate that VHb exhibits peroxidase activity, a finding in line with the hypothesis that VHb has cellular functions beyond the role as an oxygen carrier.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the detection of hemoglobins as the protein biomarkers for fecal occult blood

In this study, we discover that hemoglobins (Hb), highly water-soluble globular proteins that are the most predominant proteins detected by matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) mass spectrometry in blood, can be used as protein biomarkers for fecal occult blood (FOB). Hemoglobins were extracted from the feces with pure water and separated from the solids in feces through centrifugation. Singly charged molecular ions of Hb-related alpha chains (theoretical MW: 15 126) and beta chains (theoretical MW: 15 867) were detected by MALDI-TOF operated in linear mode using 4-hydroxy-alpha-cyanocinnamic acid (alpha-CHC) as the matrix (with a volumetric ratio of 1:1). The detection limit of FOB using this method is estimated to be lower than 0.1 microg blood per mg of feces, which is approximately 10 to 100 times lower than that of the conventional chemical approaches. The foods and dietary supplements that commonly interfere with the conventional chemical assays of FOB - such as animal blood food products and tablets containing iron and vitamin C - do not interfere with the detection of Hb biomarkers during MALDI-TOF analysis.

Enhanced oxygen releasing capacity and oxidative stress in diabetes mellitus and diabetes mellitus-associated cardiovascular disease: a comparative study

BACKGROUND

Macrovascular disease, especially cardiovascular accounts for most of the mortality in patients with type 2 diabetes mellitus. We compared oxidative stress, thermal stability and oxygen releasing capacity of hemoglobin in patients with type 2 diabetes mellitus and diabetes-associated cardiovascular disease.

METHODS

The study was performed on 38 control subjects, 31 diabetics, 36 diabetics with cardiovascular complications, and 33 non-diabetic cardiovascular subjects.

RESULTS

Enhanced oxidative stress was shown by an increased protein carbonyl content observed both in plasma and in hemolysate of the diseased samples in type 2 diabetes and diabetes-associated cardiovascular diseased patients. Altered levels of cytoprotective enzymes were shown by decreased catalase activity, increased glutathione reductase activity and unaltered superoxide dismutase activity. Peroxidative activity of diseased hemoglobin was much higher compared to healthy controls indicating possible structural changes in pathologic hemoglobin molecule as a result of disease induced oxidative stress. This result is in good agreement with the observation that thermal stability of pathologic hemoglobin was also found to be less compared to control subjects. Enhanced oxygen releasing capacity of tetrameric oxyhemoglobin was monitored in presence of the drug Trifluoperazine in pathologic red blood cells, maximum increment being noticed in diabetic cardiovascular diseased subjects.

CONCLUSION

Hyperglycemia-induced oxidative stress was responsible to affect the thermal stability and oxygen releasing capacity of hemoglobin and the effect is more pronounced in diabetes-associated cardiovascular disease.

Open reading frame yjbI of Bacillus subtilis codes for truncated hemoglobin

A hypothetical open reading frame from Bacillus subtilis genome, yjbI [NCBI genome database Accession No. ] having homology to many globin and globin-like proteins from different microbial genomes, was selectively amplified from the chromosomal DNA of B. subtilis strain DB104 based on genome sequence database of B. subtilis strain 168. The gene was cloned and over-expressed in Escherichia coli under the transcriptional control of tandem lambda P(L) and P(R) promoters, and the protein was purified to homogeneity. The single-chain monomeric hemoglobin-like protein is stable to the extent of 5.45 kcal/mol at 25 degrees C, binds carbon mono-oxide, and shows optical spectra characteristic of hemoproteins. The protein also exhibits peroxidase-like activity. This is the first report of a truncated bacterial globin endowed with peroxidase-like activity. The activity is enhanced in the presence of urea and guanidine hydrochloride, more so in the presence of the latter. Presumably, only a small portion of the protein is involved in peroxidase activity, which is exposed with increasing concentration of the denaturants.

Rat, caprine, equine and bovine erythrocyte ghosts exposed to t-butyl hydroperoxide as a model to study lipid peroxidation using a chemiluminescence assay

The aim of the present study was to analyze the time-course of t-butyl hydroperoxide-induced changes in lipid peroxidation, fatty acid composition and chemiluminescence intensity in rat, caprine, equine and bovine erythrocyte ghosts. A relatively high content of arachidonic acid (C20:4 n6) and docosahexaenoic acid (C22:6 n3) was characteristic of the rat erythrocyte ghosts. The fatty acid composition of native erythrocyte ghosts obtained from caprine, equine and bovine was characterized by a high content of oleic acid (C18:1 n9) and a low content of the peroxidable polyunsaturated fatty acids (C20:4 n6 and C22:6 n3). The proportion of linoleic acid (C18:2 n6) was higher in equine and bovine compared to rat and caprine. Increase in lipid peroxidation in rat erythrocyte ghosts was maximal within 12 min of incubation, t-butyl hydroperoxide concentration dependent and was paralleled by a decrease in C18:2 n6, C20:4 n6 and C22:6 n3 and an increase in chemiluminescence formation. Polyunsaturated fatty acids (PUFAs) present in rat erythrocyte ghosts exhibit the highest sensitivity to oxidative damaged and their sensitivity increases as a power function of the number of double bonds per fatty acid molecule. Light emission in caprine, equine and bovine erythrocyte ghosts was very low, t-butyl hydroperoxide concentration-dependent but changes in fatty acid composition were not observed. The main conclusion of this work is that a low unsaturation degree of fatty acids in erythrocyte ghosts of caprine, equine and bovine prevent the lipid peroxidation on those membranes when they are incubated with t-butyl hydroperoxide.

Hemoglobin stimulates the expression of matrix metalloproteinases, MMP-2 and MMP-9 by synovial cells: a possible cause of joint damage after intra-articular hemorrhage

Intra-articular bleeding causes degradation of articular cartilage leading to joint disorders, but the mechanisms is not well understood. The present study examined the effect of hemoglobin on the ability of synovial tissues to produce plasminogen activators and matrix metalloproteinases that play important roles in the degradation of articular cartilage. Human Hb added to primary cultures of human knee synovial cells markedly increased fibrinolytic activity and gelatinolytic activity. The fibrinolytic activity was due to an increase in uPA activity. Western blot analysis and gelatin zymography indicated that the increased gelatinolytic activity was due to increased MMP-2 and -9. In order to know whether the effect of Hb on cultured synovial tissue is also true in in vivo system or not, rabbit hemoglobin was injected into rabbit knee joints. Coinciding with in vitro study, hemoglobin elicited considerable increase in fibrinolytic and gelatinolytic activity. The level of proteoglycan fragments in the hemoglobin-treated joint fluid was significantly elevated, indicating cartilage matrix degradation. Cartilage damage after hemoglobin treatment was also confirmed by histological study. These findings suggest that hemoglobin stimulates the secretion of uPA, MMP-2 and MMP-9 by synovial tissues, and raise a possible role of hemoglobin in joint damage after intra-articular bleeding.

Role of peroxidases in Parkinson disease: a hypothesis

Extensive research has been done to elucidate the underlying molecular events causing neurodegenerative diseases such as Parkinson disease, yet the cause and the individual steps in the progression of such diseases are still unknown. Here we advance the hypothesis that, rather than or in addition to inorganic radical molecules, heme-containing peroxidase enzymes may play a major role in the etiology of Parkinson disease. This hypothesis is based on the following considerations: (1) several heme-containing enzymes with peroxidase activity are present in the substantia nigra pars compacta; (2) these peroxidases have the ability to catalyze the oxidation of proteins and lipids; (3) certain heme peroxidases are known to destroy cells in vivo; (4) heme peroxidases have the stability and specificity that could account for the fact that specific molecules and cells are subject to damage in Parkinson disease, rather than a random destruction; (5) heme peroxidase activity could account for certain reactions in connection with parkinsonism that thus far have not been adequately explained; and (6) the participation of a heme peroxidase could explain some recent observations that are inconsistent with the oxyradical theory. The peroxidase-catalyzed oxidative pathway proposed here does not preclude the participation of apoptosis as an additional mechanism for cell destruction.

Heme degradation by reactive oxygen species

Heme proteins play a major role in various biological functions, such as oxygen sensing, electron transport, signal transduction, and antioxidant defense enzymes. Most of these reactions are carried out by redox reactions of heme iron. As the heme is not recycled, most cells containing heme proteins have the microsomal mixed function oxygenase, heme oxygenase, which enzymatically degrades heme to biliverdin, carbon monoxide, and iron. However, the red cell with the largest pool of heme protein, hemoglobin, contains no heme oxygenase, and enzymatic degradation of the red cell heme occurs only after the senescent red cells are removed by the reticuloendothelial system. Therefore, only nonenzymatic heme degradation initiated when the heme iron undergoes redox reactions in the presence of oxygen-producing reactive oxygen species takes place in the red cell. Unlike enzymatic degradation, which specifically attacks the alpha-methene bridge, reactive oxygen species randomly attack all the carbon methene bridges of the tetrapyrrole rings, producing various pyrrole products in addition to releasing iron. This review focuses on the literature related to nonenzymatic heme degradation with special emphasis on hemoglobin, the dominant red cell heme protein.

Interaction of porphyrins with heme proteins--a brief review

Two important porphyrins, protoporphyrin IX and hematoporphyrin IX, derivatives of which form the basis of photosensitization in the photodynamic therapy of cancer treatment, interact with two physiologically important heme proteins hemoglobin and myoglobin. The extent and modality of these interactions vary with the state of aggregation of the two porphyrins. Upon binding with these proteins, both the drugs change the protein conformations and release the heme-bound oxygen from the oxyproteins. At the same time, the peroxidase activities of these proteins are potentiated due to the protein-porphyrin complexation, as is found in case of horseradish peroxidase also. The effect of porphyrins on heme proteins should be given due consideration in elucidating the details of the mechanism of porphyrin actions in therapy.

Protoporphyrin IX-induced structural and functional changes in human red blood cells, haemoglobin and myoglobin

Protoporphyrin IX and its derivatives are used as photosensitizers in the photodynamic therapy of cancer. Protoporphyrin IX penetrates into human red blood cells and releases oxygen from them. This leads to a change in the morphology of the cells. Spectrophotometric studies reveal that protoporphyrin IX interacts with haemoglobin and myoglobin forming ground state complexes. For both proteins, the binding affinity constant decreases, while the possible number of binding sites increases, as the aggregation state of the porphyrin is increased. The interactions lead to conformational changes of both haemoglobin and myoglobin as observed in circular dichroism studies. Upon binding with the proteins, protoporphyrin IX releases the heme-bound oxygen from the oxyproteins, which is dependent on the stoichiometric ratios of the porphyrin : protein. The peroxidase activities of haemoglobin and myoglobin are potentiated by the protein-porphyrin complexation. Possible mechanisms underlying the relation between the porphyrin-induced structural modifications of the heme proteins and alterations in their functional properties have been discussed. The findings may have a role in establishing efficacy of therapeutic uses of porphyrins as well as in elucidating their mechanisms of action as therapeutic agents.

Correlation between functional and structural changes of reduced and oxidized trout hemoglobins I and IV at different pHs. A circular dichroism study

Circular dichroism (CD) spectra of two major hemoglobin components (Hb), HbI and HbIV, from Oncorhyncus mykiss (formerly Salmo irideus) trout were evaluated in the range 250-600 nm. HbI is characterized by a complete insensitivity to pH changes, while HbIV presents the Root effect. Both reduced [iron(II) or oxy] and oxidized (met) forms of the two proteins were studied at different pHs, 7.8 and 6.0, to obtain information about the pH effects on the structural features of these hemoglobins. Data obtained show that oxy and met-HbI are almost insensitive to pH decrease, remaining in the R conformational state also at low pH. On the contrary, the pH decrease induces similar structural changes, characteristics of ligand dissociation and R-->T transition, both in the reduced and in the oxidized HbIV. The structural changes, monitored by CD, are compared with the peroxidative activity of iron(II)-Hb and met-Hb forms and with the superoxide anion scavenger capacity of the proteins.

Preparation and reactivity studies of synthetic microperoxidases containing b-type heme

In order to create a heme environment that permits biomimicry of heme-containing peroxidases, a number of new hemin-peptide complexes--hemin-2(18)-glycyl-L-histidine methyl ester (HGH), hemin-2(18)-glycyl-glycyl-L-histidine methyl ester (HGGH), and hemin-2,18-bis(glycyl-glycyl-L-histidine methyl ester) (H2GGH)--have been prepared by condensation of glycyl-L-histidine methyl ester or glycyl-glycyl-L-histidine methyl ester with the propionic side chains of hemin. Characterization by means of UV/vis- and 1H NMR spectroscopy as well as cyclic- and differential pulse voltammetry indicates the formation of five-coordinate complexes in the case of HGH and HGGH, with histidine as an axial ligand. In the case of H2GGH, a six-coordinate complex with both imidazoles coordinated to the iron center appears to be formed. However, 1H NMR of H2GGH reveals the existence of an equilibrium between low-spin six-coordinate and high-spin five-coordinate species in solution. The catalytic activity of the hemin-peptide complexes towards several organic substrates, such as p-cresol, L-tyrosine methyl ester, and ABTS, has been investigated. It was found that not only the five-coordinate HGH and HGGH complexes, but also the six-coordinate H2GGH, catalyze the oxidation of substrates by H2O2. The longer and less strained peptide arm provides the HGGH complex with a slightly higher catalytic efficiency, as compared with HGH, due to formation of more stable intermediate complexes.

Nitrotyrosine, dityrosine, and nitrotryptophan formation from metmyoglobin, hydrogen peroxide, and nitrite

The biological relevance of tyrosine nitration is a subject of much interest, because extensive evidence supports formation of 3-nitrotyrosine in vivo under a variety of different pathological conditions. Several reagents are likely to be responsible for nitration in vivo, among others peroxynitrite and nitrite in the presence of H(2)O(2)/peroxidases. In this work we show that also metmyoglobin and methemoglobin can nitrate free tyrosine in the presence of nitrite and H(2)O(2). The results of these studies are simulated rather well by using a scheme that comprehends all the possible reactions that can take place in the system. Thus, a good understanding of the factors that determine the yields is achieved. Finally, we demonstrate that the system metMb/H(2)O(2)/NO(2)(-) can also lead to the nitration of tryptophan and produces, in particular, 6-, 4-, and 5-nitrotryptophan.

Ectopic deposition of melanin pigments as detoxifying mechanism: a paradigm for basal nuclei pigmentation

Melanins are UV shielding pigments found in skin and other light exposed tissues. However, a kind of melanin, named neuromelanin (NM), is found in those deep brain loci that degenerate in Parkinson's disease (PD), where no such a function may be imagined. The NM synthetic pathway, different from the one of eumelanin based on tyrosinase, is still obscure as well as its physiological function. Here we show that under conditions of excess of toxic quinone concentration, nonmelanocytic cell strains (i.e., primary keratinocytes) may accumulate a dark cytoplasmatic pigment that proved to be a melanin. The ability of pigment deposition, possibly driven by peroxidases, is restricted to diploid cells and increases cell survival acting as a sink for potentially hazardous quinones. We suggest that in the basal nuclei, exposed to high level of catecholaminergic neurotransmitters, NM deposition is a relevant antioxidant mechanism by trapping quinones and semiquinones, thus protecting neurons from accumulating damage over many years. In this perspective, just as a hypothesis, we may imagine that PD neuron degeneration is the consequence of a reduced/abrogated ability to produce neuromelanin.

The chemistry of melatonin's interaction with reactive species

Melatonin has been shown to be an effective antioxidant in a number of experimental models both in vitro and in vivo. Considering the data available, it is now clear that the indoleamine is involved in antioxidative mechanisms more complex than originally envisaged. These range from the direct radical scavenging of a variety of radicals and reactive species to the control and/or modulation of a number of processes which may trigger a redox imbalance between antioxidant and prooxidant species. This review focuses on the direct radical scavenging activity of melatonin and provides a summary of the mechanisms of the reactions between the indoleamine and reactive species in pure chemical solutions. These actions likely account for at least some of the protective actions of melatonin under conditions of high oxidative stress.

Hematoporphyrin interacts with myoglobin and alters its functions

The binding parameters of hematoporphyrin, a photosensitizing drug used in photodynamic therapy, interacting with myoglobin, an oxygen storage protein, have been studied spectrofluorometrically and spectrophotometrically. Two concentration ranges of hematoporphyrin, representing significantly monomeric and aggregated (dimeric) states have been used. The binding affinity constant (K) decreases and the possible number of binding sites (p) increases as the porphyrin changes from significantly monomeric state to predominantly dimeric state. Titration of the protein with hematoporphyrin in a spectrophotometric study (differential spectroscopy) exhibits an isosbestic point indicating a ground state complex formation. The interaction leads to a conformational change of the protein as observed in a circular dichroism study. The hematoporphyrin-myoglobin interaction causes oxygen release from the protein and it varies with the stoichiometric ratio of the porphyrin:protein. Hematoporphyrin also increases the myoglobin-catalysed hydrogen peroxide-mediated oxidation of o-dianisidine and NADH. These findings on the effects of hematoporphrin-myoglobin interaction should be given due consideration in therapeutic uses of the porphyrin and its derivatives.

Hemoglobin components from trout (Salmo irideus): determination of their peroxidative activity

The peroxidative activity of trout hemoglobins, HbI and HbIV, which differ in their conformation, was compared with that of HbA. Artificial substrates (guaiacol and dopamine) and more physiological substrates such as model lipid membranes containing unsaturated fatty acids were used. The results indicate that all the hemoglobin molecules assayed show different levels of peroxidative activity. The capability to act as peroxidases is greater in HbIV than in HbI and HbA. In contrast, native globins did not show peroxidase activity. The different peroxidative activity of the Hbs is discussed in relation to stability both vs. protein oxidation and protein dissociation. The results confirm the view that hemoglobin may be of importance in establishing the life span of the erythrocyte itself.