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Chiara Ciaccio,
Alessandra Pesce,
Grazia R Tundo,
Lesley Tilleman,
Laura Bertolacci,
Sylvia Dewilde,
Luc Moens,
Paolo Ascenzi,
Martino Bolognesi,
Marco Nardini,
Massimo Coletta
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ABSTRACT: Functional and structural properties of protoglobin from Methanosarcina acetivorans, whose Cys(E20)101 residue was mutated to Ser (MaPgb*), and of mutants missing either the first 20N-terminal amino acids (MaPgb*-ΔN20 mutant), or the first 33N-terminal amino acids [N-terminal loop of 20 amino acids and a 13-residue Z-helix, preceding the globin fold A-helix; (MaPgb*-ΔN20Z mutant)] have been investigated. In keeping with the MaPgb*-ΔN20 mutant crystal structure, here reported at 2.0Å resolution, which shows an increased exposure of the haem propionates to the solvent, the analysis of ligand binding kinetics highlights high accessibility of ligands to the haem pocket in ferric MaPgb*-ΔN20. CO binding to ferrous MaPgb*-ΔN20 displays a marked biphasic behavior, with a fast binding process close to that observed in MaPgb* and a slow carbonylation process, characterized by a rate-limiting step. Conversely, removal of the first 33 residues induces a substantial perturbation of the overall MaPgb* structure, with loss of α-helical content and potential partial collapse of the protein chain. As such, ligand binding kinetics are characterized by very slow rates that are independent of ligand concentration, this being indicative of a high energy barrier for ligand access to the haem, possibly due to localized misfolding. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.
Biochimica et Biophysica Acta 02/2013; · 4.66 Impact Factor
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Alessio Bocedi,
Giampiero De Sanctis, Chiara Ciaccio,
Grazia R Tundo,
Alessandra Di Masi,
Gabriella Fanali,
Francesco P Nicoletti,
Mauro Fasano,
Giulietta Smulevich,
Paolo Ascenzi,
Massimo Coletta
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ABSTRACT: Human serum albumin (HSA), the most abundant protein in human plasma, could be considered as a prototypic monomeric allosteric protein, since the ligand-dependent conformational adaptability of HSA spreads beyond the immediate proximity of the binding site(s). As a matter of fact, HSA is a major transport protein in the bloodstream and the regulation of the functional allosteric interrelationships between the different binding sites represents a fundamental information for the knowledge of its transport function. Here, kinetics and thermodynamics of the allosteric modulation: (i) of carbon monoxide (CO) binding to ferrous human serum heme-albumin (HSA-heme-Fe(II)) by warfarin (WF), and (ii) of WF binding to HSA-heme-Fe(II) by CO are reported. All data were obtained at pH 7.0 and 25°C. Kinetics of CO and WF binding to the FA1 and FA7 sites of HSA-heme-Fe(II), respectively, follows a multi-exponential behavior (with the same relative percentage for the two ligands). This can be accounted for by the existence of multiple conformations and/or heme-protein axial coordination forms of HSA-heme-Fe(II). The HSA-heme-Fe(II) populations have been characterized by resonance Raman spectroscopy, indicating the coexistence of different species characterized by four-, five- and six-coordination of the heme-Fe atom. As a whole, these results suggest that: (i) upon CO binding a conformational change of HSA-heme-Fe(II) takes place (likely reflecting the displacement of an endogenous ligand by CO), and (ii) CO and/or WF binding brings about a ligand-dependent variation of the HSA-heme-Fe(II) population distribution of the various coordinating species. The detailed thermodynamic and kinetic analysis here reported allows a quantitative description of the mutual allosteric effect of CO and WF binding to HSA-heme-Fe(II).
PLoS ONE 01/2013; 8(3):e58842. · 4.09 Impact Factor
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ABSTRACT: Methanosarcina acetivorans is a strictly anaerobic non-motile methane-producing Archaea expressing protoglobin (Pgb) which might either facilitate O(2) detoxification or act as a CO sensor/supplier in methanogenesis. Unusually, Methanosarcina acetivorans Pgb (MaPgb) binds preferentially O(2) rather than CO and displays anticooperativity in ligand binding. Here, kinetics and/or thermodynamics of ferric and ferrous MaPgb (MaPgb(III) and MaPgb(II), respectively) nitrosylation are reported. Data were obtained between pH 7.2 and 9.5, at 22.0 °C. Addition of NO to MaPgb(III) leads to the transient formation of MaPgb(III)-NO in equilibrium with MaPgb(II)-NO(+). In turn, MaPgb(II)-NO(+) is converted to MaPgb(II) by OH(-)-based catalysis. Then, MaPgb(II) binds NO very rapidly leading to MaPgb(II)-NO. The rate-limiting step for reductive nitrosylation of MaPgb(III) is represented by the OH(-)-mediated reduction of MaPgb(II)-NO(+) to MaPgb(II). Present results highlight the potential role of MaPgb in scavenging of reactive nitrogen and oxygen species.
Biochemical and Biophysical Research Communications 12/2012; · 2.48 Impact Factor
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ABSTRACT: Insulin-Degrading Enzyme (IDE) is a highly conserved zinc metallopeptidase which is ubiquitously distributed in human tissues, being particularly abundant in the brain, liver and muscles. IDE activity has been historically associated to insulin and β-amyloid catabolism. However, over the last decade, several experimental findings have established that IDE is also involved in a wide variety of physiopathological processes, including ubiquitin clearance and Varicella Zoster Virus infection. In this study, we demonstrate that normal and malignant cells exposed to different stresses markedly up-regulate IDE in a Heat Shock Protein (HSP)-like fashion. Additionally, we focused our attention on tumor cells and report that (i) IDE is overexpressed in vivo in tumors of the Central Nervous System (CNS); (ii) IDE-silencing inhibits neuroblastoma (SHSY5Y) cell prolifera- tion and triggers cell death; (iii) IDE inhibition is accompanied by a decrease of the poly-ubiquitinated protein content and co-immunoprecipitates with proteasome and ubiquitin in SHSY5Y cells. In this work, we propose a novel role for IDE as a Heat-Shock Protein with implications in cell growth regulation and cancer progression, thus opening up an intriguing hypothesis of IDE as an anticancer target.
Journal of Biological Chemistry 11/2012; · 4.77 Impact Factor
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ABSTRACT: Insulin degradation is a finely tuned process that plays a major role in controlling insulin action and most evidence supports IDE (insulin-degrading enzyme) as the primary degradative agent. However, the biomolecular mechanisms involved in the interaction between IDE and its substrates are often obscure, rendering the specific enzyme activity quite difficult to target. On the other hand, biometals, such as copper, aluminum and zinc, have an important role in pathological conditions such as Alzheimer's disease or diabetes mellitus. The metabolic disorders connected with the latter lead to some metallostasis alterations in the human body and many studies point at a high level of interdependence between diabetes and several cations. We have previously reported (Grasso et al., Chem. Eur. J. 17 (2011) 2752-2762) that IDE activity toward Aβ peptides can be modulated by metal ions. Here, we have investigated the effects of different metal ions on the IDE proteolytic activity toward insulin as well as a designed peptide comprising a portion of the insulin B chain (B20-30), which has a very low affinity for metal ions. The results obtained by different experimental techniques clearly show that IDE is irreversibly inhibited by copper(I) but is still able to process its substrates when it is bound to copper(II).
Journal of inorganic biochemistry 06/2012; · 3.25 Impact Factor
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ABSTRACT: The deposition of β-amyloid (Aβ) into senile plaques and the impairment of somatostatin-mediated neurotransmission are key pathological events in the onset of Alzheimer's disease (AD). Insulin-degrading-enzyme (IDE) is one of the main extracellular protease targeting Aβ, and thus it represents an interesting pharmacological target for AD therapy. We show that the active form of somatostatin-14 regulates IDE activity by affecting its expression and secretion in microglia cells. A similar effect can also be observed when adding octreotide. Following a previous observation where somatostatin directly interacts with IDE, here we demonstrate that somatostatin regulates Aβ catabolism by modulating IDE proteolytic activity in IDE gene-silencing experiments. As a whole, these data indicate the relevant role played by somatostatin and, potentially, by analogue octreotide, in preventing Aβ accumulation by partially restoring IDE activity.
PLoS ONE 01/2012; 7(4):e34376. · 4.09 Impact Factor
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Stefania Abbruzzetti,
Lesley Tilleman,
Stefano Bruno,
Cristiano Viappiani,
Filip Desmet,
Sabine Van Doorslaer,
Massimo Coletta, Chiara Ciaccio,
Paolo Ascenzi,
Marco Nardini,
Martino Bolognesi,
Luc Moens,
Sylvia Dewilde
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ABSTRACT: Protoglobin from Methanosarcina acetivorans (MaPgb) is a dimeric globin with peculiar structural properties such as a completely buried haem and two orthogonal tunnels connecting the distal cavity to the solvent. CO binding to and dissociation from MaPgb occur through a biphasic kinetics. We show that the heterogenous kinetics arises from binding to (and dissociation from) two tertiary conformations in ligation-dependent equilibrium. Ligation favours the species with high binding rate (and low dissociation rate). The equilibrium is shifted towards the species with low binding (and high dissociation) rates for the unliganded molecules. A quantitative model is proposed to describe the observed carbonylation kinetics.
PLoS ONE 01/2012; 7(3):e33614. · 4.09 Impact Factor
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ABSTRACT: Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.
Molecular Aspects of Medicine 11/2011; 33(2):119-208. · 9.97 Impact Factor
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ABSTRACT: Carboxymethylation of equine heart cytochrome c (cytc) changes its tertiary structure by disrupting the heme-Fe-Met80 distal bond, such that carboxymethylated cytc (CM-cytc) displays myoglobin-like properties. Here, the effect of cardiolipin (CL) on peroxynitrite isomerization by ferric CM-cytc (CM-cytc-Fe(III)) is reported. Unlike native ferric cytc (cytc-Fe(III)), CM-cytc-Fe(III) catalyzes peroxynitrite isomerization, the value of the second order rate constant (k(on)) is 6.8 × 10(4)M(-1)s(-1). However, CM-cytc-Fe(III) is less effective in peroxynitrite isomerization than CL-bound cytc-Fe(III) (CL-cytc-Fe(III); k(on)=3.2 × 10(5)M(-1)s(-1)). Moreover, CL binding to CM-cytc-Fe(III) facilitates peroxynitrite isomerization (k(on)=5.3 × 10(5)M(-1)s(-1)). Furthermore, the value of the dissociation equilibrium constant for CL binding to CM-cytc-Fe(III) (K=1.8 × 10(-5)M) is lower than that reported for CL-cytc-Fe(III) complex formation (K=5.1 × 10(-5)M). Although CM-cytc-Fe(III) and CL-cytc-Fe(III) display a different heme distal geometry and heme-Fe(III) reactivity, the heme pocket and the CL cleft are allosterically linked.
Biochemical and Biophysical Research Communications 10/2011; 415(3):463-7. · 2.48 Impact Factor
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Yu Cao,
Francesco P Nicoletti,
Giampiero De Sanctis,
Alessio Bocedi, Chiara Ciaccio,
Francesca Gullotta,
Gabriella Fanali,
Grazia R Tundo,
Alessandra di Masi,
Mauro Fasano,
Giulietta Smulevich,
Paolo Ascenzi,
Massimo Coletta
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ABSTRACT: Human serum albumin (HSA), the most prominent protein in plasma, is best known for its exceptional ligand binding capacity. HSA participates in heme scavenging by binding the macrocycle at fatty acid site 1. In turn, heme endows HSA with globin-like reactivity and spectroscopic properties. A detailed pH-dependent kinetic and spectroscopic investigation of iron(II) heme-HSA and of its carbonylated form is reported here. Iron (II) heme-HSA is a mixture of a four-coordinate intermediate-spin species (predominant at pH 5.8 and 7.0), a five-coordinate high-spin form (mainly at pH 7.0), and a six-coordinate low-spin species (predominant at pH 10.0). The acidic-to-alkaline reversible transition reflects conformational changes leading to the coordination of the heme Fe(II) atom by the His146 residue via its nitrogen atom, both in the presence and in the absence of CO. The presence of several species accounts for the complex, multiexponential kinetics observed and reflects the very slow interconversion between the different species observed both for CO association to the free iron(II) heme-HSA and for CO dissociation from CO-iron(II) heme-HSA as a function of pH.
European Journal of Biochemistry 09/2011; 17(1):133-47. · 3.42 Impact Factor
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ABSTRACT: The spectroscopic and ligand-binding properties of a 2/2 globin from the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 have been studied in the ferrous state. It displays two major conformations characterized by CO-association rates that differ by a factor of 20, with relative fractions that depend on pH. A dynamic equilibrium is found between the two conformations, as indicated by an enhanced slower phase when lower CO levels were used to allow a longer time to facilitate the transition. The deoxy form, in the absence of external ligands, is a mixture of a predominant six-coordinate low spin form and a five-coordinate high-spin state; the proportion of low spin increasing at alkaline pH. In addition, at temperatures above the physiological temperature of 1 °C, an enhanced tendency of the protein to oxidize is observed.
International Union of Biochemistry and Molecular Biology Life 07/2011; 63(7):566-73. · 3.51 Impact Factor
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ABSTRACT: Protoglobin from Methanosarcina acetivorans C2A (MaPgb), a strictly anaerobic methanogenic Archaea, displays peculiar structural and functional properties within members of the hemoglobin superfamily. In fact, MaPgb-specific loops and a N-terminal extension (20 amino acid residues) completely bury the heme within the protein matrix. Therefore, the access of diatomic gaseous molecules to the heme is granted by two apolar tunnels reaching the heme distal site from locations at the B/G and B/E helix interfaces. The presence of two tunnels within the protein matrix could be partly responsible for the slightly biphasic ligand binding behavior. Unusually, MaPgb oxygenation is favored with respect to carbonylation. Here, the crucial role of Tyr(B10)61 and Ile(G11)149 residues, located in the heme distal site and lining the protein matrix tunnels 1 and 2, respectively, on ligand binding to the heme-Fe-atom and on distal site structural organization is reported. In particular, tunnel 1 accessibility is modulated by a complex reorganization of the Trp(B9)60 and Phe(E11)93 side-chains, triggered by mutations of the Tyr(B10)61 and Ile(G11)149 residues, and affected by the presence and type of the distal heme-bound ligand.
International Union of Biochemistry and Molecular Biology Life 05/2011; 63(5):287-94. · 3.51 Impact Factor
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ABSTRACT: Protoglobin from Methanosarcina acetivorans C2A (MaPgb), a strictly anaerobic methanogenic Archaea, displays peculiar structural and functional properties within members of the hemoglobin superfamily. In fact, MaPgb-specific loops and a N-terminal extension (20 amino acid residues) completely bury the heme within the protein matrix. Therefore, the access of diatomic gaseous molecules to the heme is granted by two apolar tunnels reaching the heme distal site from locations at the B/G and B/E helix interfaces. The presence of two tunnels within the protein matrix could be partly responsible for the slightly biphasic ligand binding behavior. Unusually, MaPgb oxygenation is favored with respect to carbonylation. Here, the crucial role of Tyr(B10)61 and Ile(G11)149 residues, located in the heme distal site and lining the protein matrix tunnels 1 and 2, respectively, on ligand binding to the heme-Fe-atom and on distal site structural organization is reported. In particular, tunnel 1 accessibility is modulated by a complex reorganization of the Trp(B9)60 and Phe(E11)93 side-chains, triggered by mutations of the Tyr(B10)61 and Ile(G11)149 residues, and affected by the presence and type of the distal heme-bound ligand.
International Union of Biochemistry and Molecular Biology Life 05/2011; 63(5):spcone. · 3.51 Impact Factor
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ABSTRACT: Accumulation of neurotoxic amyloid-β peptide (Aβ) and alteration of metal homeostasis (metallostasis) in the brain are two main factors that have been very often associated with neurodegenerative diseases, such as Alzheimer's disease (AD). Aβ is constantly produced from the amyloidprecursor-protein APP precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Aβ and/or metal ions seems to lead to a pathological deposition. Although insulin-degrading enzyme (IDE) is the main metalloprotease involved in Aβ degradation in the brain being up-regulated in some areas of AD brains, the role of IDE for the onset and development of AD is far from being understood. Moreover, the biomolecular mechanisms involved in the recognition and interaction between IDE and its substrates are still obscure. In spite of the important role of metals (such as copper, aluminum, and zinc), which has brought us to propose a "metal hypothesis of AD", a targeted study of the effect of metallostasis on IDE activity has never been carried out. In this work, we have investigated the role that various metal ions (i.e., Cu(2+), Cu(+), Zn(2+), Ag(+), and Al(3+)) play in modulating the interaction between IDE and two Aβ peptide fragments, namely Aβ(1-16) and Aβ(16-28). It was therefore possible to identify the direct effect that such metal ions have on IDE structure and enzymatic activity without interferences caused by metal-induced substrate modifications. Mass spectrometry and kinetic studies revealed that, among all the metal ions tested, only Cu(2+), Cu(+), and Ag(+) have an inhibitory effect on IDE activity. Moreover, the inhibition of copper(II) is reversed by adding zinc(II), whereas the monovalent cations affect the enzyme activity irreversibly. The molecular basis of their action on the enzyme is also discussed on the basis of computational investigations.
Chemistry 02/2011; 17(9):2752-62. · 5.93 Impact Factor
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ABSTRACT: Upon interaction with bovine heart cardiolipin (CL), horse heart cytochrome c (cytc) changes its tertiary structure disrupting the heme-Fe-Met80 distal bond, reduces drastically the midpoint potential out of the range required for its physiological role, binds CO and NO with high affinity, and displays peroxidase activity. Here, the effect of CL on peroxynitrite isomerization by ferric cytc (cytc-Fe(III)) is reported. In the absence of CL, hexa-coordinated cytc does not catalyze peroxynitrite isomerization. In contrast, CL facilitates cytc-Fe(III)-mediated isomerization of peroxynitrite in a dose-dependent fashion inducing the penta-coordination of the heme-Fe(III)-atom. The value of the second order rate constant for CL-cytc-Fe(III)-mediated isomerization of peroxynitrite (k(on)) is (3.2±0.4)×10(5) M(-1) s(-1). The apparent dissociation equilibrium constant for CL binding to cytc-Fe(III) is (5.1±0.8)×10(-5) M. These results suggest that CL-cytc could play either pro-apoptotic or anti-apoptotic effects facilitating lipid peroxidation and scavenging of reactive nitrogen species, such as peroxynitrite, respectively.
Biochemical and Biophysical Research Communications 01/2011; 404(1):190-4. · 2.48 Impact Factor
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Barry D Howes,
Daniela Giordano,
Leonardo Boechi,
Roberta Russo,
Simona Mucciacciaro, Chiara Ciaccio,
Federica Sinibaldi,
Maria Fittipaldi,
Marcelo A Martí,
Darío A Estrin,
Guido di Prisco,
Massimo Coletta,
Cinzia Verde,
Giulietta Smulevich
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ABSTRACT: The genome of the cold-adapted bacterium Pseudoalteromonas haloplanktis TAC125 contains multiple genes encoding three distinct monomeric hemoglobins exhibiting a 2/2 α-helical fold. In the present work, one of these hemoglobins is studied by resonance Raman, electronic absorption and electronic paramagnetic resonance spectroscopies, kinetic measurements, and different bioinformatic approaches. It is the first cold-adapted bacterial hemoglobin to be characterized. The results indicate that this protein belongs to the 2/2 hemoglobin family, Group II, characterized by the presence of a tryptophanyl residue on the bottom of the heme distal pocket in position G8 and two tyrosyl residues (TyrCD1 and TyrB10). However, unlike other bacterial hemoglobins, the ferric state, in addition to the aquo hexacoordinated high-spin form, shows multiple hexacoordinated low-spin forms, where either TyrCD1 or TyrB10 can likely coordinate the iron. This is the first example in which both TyrCD1 and TyrB10 are proposed to be the residues that are alternatively involved in heme hexacoordination by endogenous ligands.
European Journal of Biochemistry 11/2010; 16(2):299-311. · 3.42 Impact Factor
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ABSTRACT: Cyanide binds to ferric heme-proteins with a very high affinity, reflecting the very low dissociation rate constant (k(off)). Since no techniques are available to estimate k(off), we report herewith a method to determine k(off) based on the irreversible reductive nitrosylation reaction to trap ferric myoglobin (Mb(III)). The k(off) value for cyanide dissociation from ferric cyanide horse heart myoglobin (Mb(III)-cyanide) was determined at pH 9.2 and 20.0 degrees C. Mixing Mb(III)-cyanide and NO solutions brings about absorption spectral changes reflecting the disappearance of Mb(III)-cyanide with the concomitant formation of ferrous nitrosylated Mb. Since kinetics of reductive nitrosylation of Mb(III) is much faster than Mb(III)-cyanide dissociation, the k(off) value, representing the rate-limiting step, can be directly determined. The k(off) value obtained experimentally matches very well to that calculated from values of the second-order rate constant (k(on)) and of the dissociation equilibrium constant (K) for cyanide binding to Mb(III) (k(off)=k(on)xK).
Biochemical and Biophysical Research Communications 03/2010; 393(2):196-200. · 2.48 Impact Factor
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ABSTRACT: Human serum albumin (HSA) participates in heme scavenging; in turn, heme endows HSA with myoglobin-like reactivity and spectroscopic properties. Here, the allosteric effect of ibuprofen on peroxynitrite isomerization to NO(3)(-) catalyzed by ferric human serum heme-albumin (HSA-heme-Fe(III)) is reported. Data were obtained at 22.0 degrees C. HSA-heme-Fe(III) catalyzes peroxynitrite isomerization in the absence and presence of CO(2); the values of the second order catalytic rate constant (k(on)) are 4.1 x 10(5) and 4.5 x 10(5) m(-1) s(-1), respectively. Moreover, HSA-heme-Fe(III) prevents peroxynitrite-mediated nitration of free added l-tyrosine. The pH dependence of k(on) (pK(a) = 6.9) suggests that peroxynitrous acid reacts preferentially with the heme-Fe(III) atom, in the absence and presence of CO(2). The HSA-heme-Fe(III)-catalyzed isomerization of peroxynitrite has been ascribed to the reactive pentacoordinated heme-Fe(III) atom. In the absence and presence of CO(2), ibuprofen impairs dose-dependently peroxynitrite isomerization by HSA-heme-Fe(III) and facilitates the nitration of free added l-tyrosine; the value of the dissociation equilibrium constant for ibuprofen binding to HSA-heme-Fe(III) (L) ranges between 7.7 x 10(-4) and 9.7 x 10(-4) m. Under conditions where [ibuprofen] is >L, the kinetics of HSA-heme-Fe(III)-catalyzed isomerization of peroxynitrite is superimposable to that obtained in the absence of HSA-heme-Fe(III) or in the presence of non-catalytic HSA-heme-Fe(III)-cyanide complex and HSA. Ibuprofen binding impairs allosterically peroxynitrite isomerization by HSA-heme-Fe(III), inducing the hexacoordination of the heme-Fe(III) atom. These results represent the first evidence for peroxynitrite isomerization by HSA-heme-Fe(III), highlighting the allosteric modulation of HSA-heme-Fe(III) reactivity by heterotropic interaction(s), and outlining the role of drugs in modulating HSA functions. The present results could be relevant for the drug-dependent protective role of HSA-heme-Fe(III) in vivo.
Journal of Biological Chemistry 10/2009; 284(45):31006-17. · 4.77 Impact Factor
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ABSTRACT: Globins protect from the oxidative and nitrosative cell damage. Here, kinetics of peroxynitrite scavenging by ferryl sperm whale myoglobin (MbFe(IV)O) and human hemoglobin (HbFe(IV)O), between pH 5.8 and 8.3 at 20.0 degrees C, are reported. In the absence of CO(2), values of the second-order rate constant for peroxynitrite scavenging by MbFe(IV)O and HbFe(IV)O (i.e., for MbFe(III) and HbFe(III) formation; k(on)) are 4.6 x 10(4)M(-1)s(-1) and 3.3 x 10(4)M(-1)s(-1), respectively, at pH 7.1. Values of k(on) increase on decreasing pH with pK(a) values of 6.9 and 6.7, this suggests that the ONOOH species reacts preferentially with MbFe(IV)O and HbFe(IV)O. In the presence of CO(2) (=1.2 x 10(-3)M), values of k(on) for peroxynitrite scavenging by MbFe(IV)O and HbFe(IV)O are essentially pH-independent, the average k(on) values are 7.1 x 10(4)M(-1)s(-1) and 1.2 x 10(5)M(-1)s(-1), respectively. As a whole, MbFe(IV)O and HbFe(IV)O, obtained by treatment with H(2)O(2), undertake within the same cycle H(2)O(2) and peroxynitrite detoxification.
Biochemical and Biophysical Research Communications 09/2009; 390(1):27-31. · 2.48 Impact Factor
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ABSTRACT: Globins are generally considered as carriers of diatomic gaseous ligands (e.g., O(2) and NO) in metazoa. Recently, the (pseudo-)enzymatic activity of globins towards reactive nitrogen and oxygen species has been elucidated. In particular, some globins (e.g., hemoglobin and myoglobin) catalyze the enzymatic scavenging of NO and peroxynitrite in the presence of H(2)O(2). Indeed, H(2)O(2) oxidizes some globins leading to the formation of water and of the heme-protein ferryl derivative, which, in turn, oxidizes NO and peroxynitrite leading to the formation of the globin ferric species, NO(2)(-), and NO(3)(-). Here, we hypothesize that NO, peroxynitrite, and H(2)O(2) are co-substrates for the peroxidase activity of some globins, this catalytic activity was reported in 1900 for the first time, even though the substrates have never been identified firmly up to now.
International Union of Biochemistry and Molecular Biology Life 02/2009; 61(1):62-73. · 3.51 Impact Factor
