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Su Y, Majtan T, Freeman KM, Linck R, Ponter S, Kraus JP, Burstyn JN. Comparative study of enzyme activity and heme reactivity in Drosophila melanogaster and Homo sapiens cystathionine β-synthases. Biochemistry 2013; 52:741-51. [PMID: 23002992 PMCID: PMC3751582 DOI: 10.1021/bi300615c] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cystathionine β-synthase (CBS) is the first and rate-limiting enzyme in the transsulfuration pathway, which is critical for the synthesis of cysteine from methionine in eukaryotes. CBS uses coenzyme pyridoxal 5'-phosphate (PLP) for catalysis, and S-adenosylmethionine regulates the activity of human CBS, but not yeast CBS. Human and fruit fly CBS contain heme; however, the role for heme is not clear. This paper reports biochemical and spectroscopic characterization of CBS from fruit fly Drosophila melanogaster (DmCBS) and the CO/NO gas binding reactions of DmCBS and human CBS. Like CBS enzymes from lower organisms (e.g., yeast), DmCBS is intrinsically highly active and is not regulated by AdoMet. The DmCBS heme coordination environment, the reactivity, and the accompanying effects on enzyme activity are similar to those of human CBS. The DmCBS heme bears histidine and cysteine axial ligands, and the enzyme becomes inactive when the cysteine ligand is replaced. The Fe(II) heme in DmCBS is less stable than that in human CBS, undergoing more facile reoxidation and ligand exchange. In both CBS proteins, the overall stability of the protein is correlated with the heme oxidation state. Human and DmCBS Fe(II) hemes react relatively slowly with CO and NO, and the rate of the CO binding reaction is faster at low pH than at high pH. Together, the results suggest that heme incorporation and AdoMet regulation in CBS are not correlated, possibly providing two independent means for regulating the enzyme.
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Affiliation(s)
- Yang Su
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin, 53706 USA
| | - Tomas Majtan
- Department of Pediatrics, University of Colorado, Denver, Aurora, Colorado 80045
- Department of Genomics & Biotechnology, Institute of Molecular Biology SAS, Dubravska cesta 21, Bratislava, 84551, Slovakia
| | - Katherine M. Freeman
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin, 53706 USA
| | - Rachel Linck
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin, 53706 USA
| | - Sarah Ponter
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin, 53706 USA
| | - Jan P. Kraus
- Department of Pediatrics, University of Colorado, Denver, Aurora, Colorado 80045
| | - Judith N. Burstyn
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin, 53706 USA
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Bovine Carbonyl Lactoperoxidase Structure at 2.0Å Resolution and Infrared Spectra as a Function of pH. Protein J 2012; 31:598-608. [DOI: 10.1007/s10930-012-9436-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Mack ET, Snyder PW, Perez-Castillejos R, Bilgiçer B, Moustakas DT, Butte MJ, Whitesides GM. Dependence of avidity on linker length for a bivalent ligand-bivalent receptor model system. J Am Chem Soc 2012; 134:333-45. [PMID: 22088143 PMCID: PMC3272676 DOI: 10.1021/ja2073033] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper describes a synthetic dimer of carbonic anhydrase, and a series of bivalent sulfonamide ligands with different lengths (25 to 69 Å between the ends of the fully extended ligands), as a model system to use in examining the binding of bivalent antibodies to antigens. Assays based on analytical ultracentrifugation and fluorescence binding indicate that this system forms cyclic, noncovalent complexes with a stoichiometry of one bivalent ligand to one dimer. This dimer binds the series of bivalent ligands with low picomolar avidities (K(d)(avidity) = 3-40 pM). A structurally analogous monovalent ligand binds to one active site of the dimer with K(d)(mono) = 16 nM. The bivalent association is thus significantly stronger (K(d)(mono)/K(d)(avidity) ranging from ~500 to 5000 unitless) than the monovalent association. We infer from these results, and by comparison of these results to previous studies, that bivalency in antibodies can lead to associations much tighter than monovalent associations (although the observed bivalent association is much weaker than predicted from the simplest level of theory: predicted K(d)(avidity) of ~0.002 pM and K(d)(mono)/K(d)(avidity) ~ 8 × 10(6) unitless).
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Affiliation(s)
- Eric T. Mack
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Phillip W. Snyder
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Raquel Perez-Castillejos
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Başar Bilgiçer
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Demetri T. Moustakas
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Manish J. Butte
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - George M. Whitesides
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
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Time resolved thermodynamics associated with ligand photorelease in heme peroxidases and globins: Open access channels versus gated ligand release. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:1065-76. [PMID: 21278003 DOI: 10.1016/j.bbapap.2011.01.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2010] [Revised: 01/14/2011] [Accepted: 01/17/2011] [Indexed: 10/18/2022]
Abstract
Heme proteins represent a diverse class of biomolecules responsible for an extremely diverse array of physiological functions including electron transport, monooxygenation, ligand transport and storage, cellular signaling, respiration, etc. An intriguing aspect of these proteins is that such functional diversity is accomplished using a single type of heme macrocycle based upon iron protoporphyrin IX. The functional diversity originates from a delicate balance of inter-molecular interactions within the protein matrix together with well choreographed dynamics that modulate the heme electronic structure as well as ligand entry/exit pathways from the bulk solvent to the active site. Of particular interest are the dynamics and energetics associated with the entry/exit of ligands as this process plays a significant role in regulating the rates of heme protein activity. Time-resolved photoacoustic calorimetry (PAC) has emerged as a powerful tool through which to probe the underlying energetics associated with small molecule dissociation and release to the bulk solvent in heme proteins on time scales from tens of nanoseconds to several microseconds. In this review, the results of PAC studies on various classes of heme proteins are summarized highlighting how different protein structures affect the thermodynamics of ligand migration. This article is part of a Special Issue entitled: Protein Dynamics: Experimental and Computational Approaches.
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Murphy EJ, Maréchal A, Segal AW, Rich PR. CO binding and ligand discrimination in human myeloperoxidase. Biochemistry 2010; 49:2150-8. [PMID: 20146436 DOI: 10.1021/bi9021507] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Despite the fact that ferrous myeloperoxidase (MPO) can bind both O(2) and NO, its ability to bind CO has been questioned. UV/visible spectroscopy was used to confirm that CO induces small spectral shifts in ferrous MPO, and Fourier transform infrared difference spectroscopy showed definitively that these arose from formation of a heme ferrous-CO compound. Recombination rates after CO photolysis were monitored at 618 and 645 nm as a function of CO concentration and pH. At pH 6.3, k(on) and k(off) were 0.14 mM(-1) x s(-1) and 0.23 s(-1), respectively, yielding an unusually high K(D) of 1.6 mM. This affinity of MPO for CO is 10 times weaker than its affinity for O(2). The observed rate constant for CO binding increased with increasing pH and was governed by a single protonatable group with a pK(a) of 7.8. Fourier transform infrared spectroscopy revealed two different conformations of bound CO with frequencies at 1927 and 1942 cm(-1). Their recombination rate constants were identical, indicative of two forms of bound CO that are in rapid thermal equilibrium rather than two distinct protein populations with different binding sites. The ratio of bound states was pH-dependent (pK(a) approximately 7.4) with the 1927 cm(-1) form favored at high pH. Structural factors that account for the ligand-binding properties of MPO are identified by comparisons with published data on a range of other ligand-binding heme proteins, and support is given to the recent suggestion that the proximal His336 in MPO is in a true imidazolate state.
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Affiliation(s)
- Emma J Murphy
- Centre for Molecular Medicine, Division of Medicine, University College London, 5 University Street, London WC1E 6JJ, UK
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Zelent B, Sharp KA, Vanderkooi JM. Differential scanning calorimetry and fluorescence study of lactoperoxidase as a function of guanidinium-HCl, urea, and pH. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:1508-15. [PMID: 20298816 DOI: 10.1016/j.bbapap.2010.03.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 03/03/2010] [Accepted: 03/05/2010] [Indexed: 10/19/2022]
Abstract
The stability of bovine lactoperoxidase to denaturation by guanidinium-HCl, urea, or high temperature was examined by differential scanning calorimetry (DSC) and tryptophan fluorescence. The calorimetric scans were observed to be dependent on the heating scan rate, indicating that lactoperoxidase stability at temperatures near Tm is controlled by kinetics. The values for the thermal transition, Tm, at slow heating scan rate were 66.8, 61.1, and 47.2 degrees C in the presence of 0.5, 1, and 2 M guanidinium-HCl, respectively. The extrapolated value for Tm in the absence of guanidinium-HCl is 73.7 degrees C, compared with 70.2 degrees C obtained by experiment; a lower experimental value without a denaturant is consistent with distortion of the thermal profile due to aggregation or other irreversible phenomenon. Values for the heat capacity, Cp, at Tm and Ea for the thermal transition decrease under conditions where Tm is lowered. At a given concentration, urea is less effective than guanidinium-HCl in reducing Tm, but urea reduces Cp relatively more. Both fluorescence and DSC indicate that thermally denatured protein is not random coil. A change in fluorescence around 35 degrees C, which was previously reported for EPR and CD measurements (Boscolo et al. Biochim. Biophys. Acta 1774 (2007) 1164-1172), is not seen by calorimetry, suggesting that a local and not a global change in protein conformation produces this fluorescence change.
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Affiliation(s)
- Bogumil Zelent
- Department of Biochemistry & Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
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Battistuzzi G, Bellei M, Bortolotti CA, Sola M. Redox properties of heme peroxidases. Arch Biochem Biophys 2010; 500:21-36. [PMID: 20211593 DOI: 10.1016/j.abb.2010.03.002] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Revised: 03/01/2010] [Accepted: 03/02/2010] [Indexed: 10/19/2022]
Abstract
Peroxidases are heme enzymes found in bacteria, fungi, plants and animals, which exploit the reduction of hydrogen peroxide to catalyze a number of oxidative reactions, involving a wide variety of organic and inorganic substrates. The catalytic cycle of heme peroxidases is based on three consecutive redox steps, involving two high-valent intermediates (Compound I and Compound II), which perform the oxidation of the substrates. Therefore, the thermodynamics and the kinetics of the catalytic cycle are influenced by the reduction potentials of three redox couples, namely Compound I/Fe3+, Compound I/Compound II and Compound II/Fe3+. In particular, the oxidative power of heme peroxidases is controlled by the (high) reduction potential of the latter two couples. Moreover, the rapid H2O2-mediated two-electron oxidation of peroxidases to Compound I requires a stable ferric state in physiological conditions, which depends on the reduction potential of the Fe3+/Fe2+ couple. The understanding of the molecular determinants of the reduction potentials of the above redox couples is crucial for the comprehension of the molecular determinants of the catalytic properties of heme peroxidases. This review provides an overview of the data available on the redox properties of Fe3+/Fe2+, Compound I/Fe3+, Compound I/Compound II and Compound II/Fe3+ couples in native and mutated heme peroxidases. The influence of the electron donor properties of the axial histidine and of the polarity of the heme environment is analyzed and the correlation between the redox properties of the heme group with the catalytic activity of this important class of metallo-enzymes is discussed.
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Affiliation(s)
- Gianantonio Battistuzzi
- Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41100 Modena, Italy.
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Sheikh IA, Singh AK, Singh N, Sinha M, Singh SB, Bhushan A, Kaur P, Srinivasan A, Sharma S, Singh TP. Structural evidence of substrate specificity in mammalian peroxidases: structure of the thiocyanate complex with lactoperoxidase and its interactions at 2.4 A resolution. J Biol Chem 2009; 284:14849-56. [PMID: 19339248 PMCID: PMC2685666 DOI: 10.1074/jbc.m807644200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2008] [Revised: 03/18/2009] [Indexed: 11/06/2022] Open
Abstract
The crystal structure of the complex of lactoperoxidase (LPO) with its physiological substrate thiocyanate (SCN(-)) has been determined at 2.4A resolution. It revealed that the SCN(-) ion is bound to LPO in the distal heme cavity. The observed orientation of the SCN(-) ion shows that the sulfur atom is closer to the heme iron than the nitrogen atom. The nitrogen atom of SCN(-) forms a hydrogen bond with a water (Wat) molecule at position 6'. This water molecule is stabilized by two hydrogen bonds with Gln(423) N(epsilon2) and Phe(422) oxygen. In contrast, the placement of the SCN(-) ion in the structure of myeloperoxidase (MPO) occurs with an opposite orientation, in which the nitrogen atom is closer to the heme iron than the sulfur atom. The site corresponding to the positions of Gln(423), Phe(422) oxygen, and Wat(6)' in LPO is occupied primarily by the side chain of Phe(407) in MPO due to an entirely different conformation of the loop corresponding to the segment Arg(418)-Phe(431) of LPO. This arrangement in MPO does not favor a similar orientation of the SCN(-) ion. The orientation of the catalytic product OSCN(-) as reported in the structure of LPO.OSCN(-) is similar to the orientation of SCN(-) in the structure of LPO.SCN(-). Similarly, in the structure of LPO.SCN(-).CN(-), in which CN(-) binds at Wat(1), the position and orientation of the SCN(-) ion are also identical to that observed in the structure of LPO.SCN.
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Affiliation(s)
- Ishfaq Ahmed Sheikh
- Department of Biophysics, All India Institute of Medical Sciences, New Delhi 110 029, India
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Zederbauer M, Furtmüller PG, Brogioni S, Jakopitsch C, Smulevich G, Obinger C. Heme to protein linkages in mammalian peroxidases: impact on spectroscopic, redox and catalytic properties. Nat Prod Rep 2007; 24:571-84. [PMID: 17534531 DOI: 10.1039/b604178g] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Martina Zederbauer
- BOKU-University of Natural Resources and Applied Life Sciences, Department of Chemistry, Division of Biochemistry, Muthgasse 18, A-1190 Vienna, Austria
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Lockney D, Miksovská J. Characterization of carbon monoxide photodissociation from Fe(II)LPO with photoacoustic calorimetry. J Phys Chem B 2007; 110:24165-70. [PMID: 17125388 DOI: 10.1021/jp0641233] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Lactoperoxidase belongs to a family of mammalian peroxidases that catalyze the oxidation of halides and small organic molecules in the presence of H2O2. We have used photoacoustic calorimetry to characterize thermodynamic parameters associated with ligand dissociation from bovine milk lactoperoxidase. Upon CO photorelease, a prompt (tau < 50 ns) exothermic volume contraction (DeltaH = -20 +/- 7 kcal mol-1 and DeltaH = -2 +/- 1 mL mol-1) was measured at pH 7.0 and 4.0, whereas an endothermic expansion (DeltaH = 30 +/- 13 kcal mol-1 and DeltaV = 9 +/- 2 mL mol(-1)) was observed at pH 10.0 and 7.0 in the presence of 500 mM NaCl. We attribute the observed volume and enthalpy changes to electrostriction arising from changes in the charge distribution associated with a reorganization of the heme binding pocket upon ligand dissociation. It is likely that cleavage of the Fe-CO bond is accompanied by distortion of a salt bridge between Arg557 and the heme propionate group, resulting in the observed electrostriction due to changes in charge distribution.
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Affiliation(s)
- Dustin Lockney
- Chemistry Department, Marshall University, One John Marshall Drive, Huntington, West Virginia 25755, USA
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Fischer H, Widdicombe JH. Mechanisms of acid and base secretion by the airway epithelium. J Membr Biol 2006; 211:139-50. [PMID: 17091214 PMCID: PMC2929530 DOI: 10.1007/s00232-006-0861-0] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2006] [Revised: 04/15/2006] [Indexed: 12/15/2022]
Abstract
One of the main functions of the airway epithelium is to inactivate and remove infectious particles from inhaled air and thereby prevent infection of the distal lung. This function is achieved by mucociliary and cough clearance and by antimicrobial factors present in the airway surface liquid (ASL). There are indications that airway defenses are affected by the pH of the ASL and historically, acidification of the airway surfaces has been suggested as a measure of airway disease. However, even in health, the ASL is slightly acidic, and this acidity might be part of normal airway defense. Only recently research has focused on the mechanisms responsible for acid and base secretion into the ASL. Advances resulted from research into the airway disease associated with cystic fibrosis (CF) after it was found that the CFTR Cl(-) channel conducts HCO (3) (-) and, therefore, may contribute to ASL pH. However, the acidity of the ASL indicated parallel mechanisms for H(+) secretion. Recent investigations identified several H(+) transporters in the apical membrane of the airway epithelium. These include H(+) channels and ATP-driven H(+) pumps, including a non-gastric isoform of the H(+)-K(+) ATPase and a vacuolar-type H(+) ATPase. Current knowledge of acid and base transporters and their potential roles in airway mucosal pH regulation is reviewed here.
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Affiliation(s)
- Horst Fischer
- Children's Hospital Oakland Research Institute, Oakland, CA 94609, USA.
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De Sanctis G, Fasciglione GF, Marini S, Sinibaldi F, Santucci R, Monzani E, Dallacosta C, Casella L, Coletta M. pH-dependent redox and CO binding properties of chelated protoheme-l-histidine and protoheme-glycyl-l-histidine complexes. J Biol Inorg Chem 2005; 11:153-67. [PMID: 16341900 DOI: 10.1007/s00775-005-0060-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Accepted: 11/04/2005] [Indexed: 10/25/2022]
Abstract
The pH dependence of redox properties, spectroscopic features and CO binding kinetics for the chelated protohemin-6(7)-L-histidine methyl ester (heme-H) and the chelated protohemin-6(7)-glycyl-L-histidine methyl ester (heme-GH) systems has been investigated between pH 2.0 and 12.0. The two heme systems appear to be modulated by four protonating groups, tentatively identified as coordinated H(2)O, one of heme's propionates, N(epsilon) of the coordinating imidazole, and the carboxylate of the histidine residue upon hydrolysis of the methyl ester group (in acid medium). The pK (a) values are different for the two hemes, thus reflecting structural differences. In particular, the different strain at the Fe-N(epsilon) bond, related to the different length of the coordinating arm, results in a dramatic alteration of the bond strength, which is much smaller in heme-H than in heme-GH. It leads to a variation in the variation of the pKa for the protonation of the N(epsilon) of the axial imidazole as well as in the proton-linked behavior of the other protonating groups, envisaging a cross-talk communication mechanism among different groups of the heme, which can be operative and relevant also in the presence of the protein matrix.
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Affiliation(s)
- Giampiero De Sanctis
- Department of Molecular, Cellular and Animal Biology, University of Camerino, Via F. Camerini 2, 62032 Camerino, Italy
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Jantschko W, Furtmüller PG, Zederbauer M, Neugschwandtner K, Jakopitsch C, Obinger C. Reaction of ferrous lactoperoxidase with hydrogen peroxide and dioxygen: an anaerobic stopped-flow study. Arch Biochem Biophys 2005; 434:51-9. [PMID: 15629108 DOI: 10.1016/j.abb.2004.10.014] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2004] [Revised: 10/14/2004] [Indexed: 11/19/2022]
Abstract
Lactoperoxidase (LPO) is found in mucosal surfaces and exocrine secretions including milk, tears, and saliva and has physiological significance in antimicrobial defense which involves (pseudo-)halide oxidation. LPO compound III (a ferrous-dioxygen complex) is known to be formed rapidly by an excess of hydrogen peroxide and could participate in the observed catalase-like activity of LPO. The present anaerobic stopped-flow kinetic analysis was performed in order to elucidate the catalytic mechanism of LPO and the kinetics of compound III formation by probing the reactivity of ferrous LPO with hydrogen peroxide and molecular oxygen. It is shown that ferrous LPO heterolytically cleaves hydrogen peroxide forming water and oxyferryl LPO (compound II). The two-electron oxidation reaction follows second-order kinetics with the apparent bimolecular rate constant being (7.2+/-0.3) x 10(4) M(-1) s(-1) at pH 7.0 and 25 degrees C. The H2O2-mediated conversion of compound II to compound III follows also second-order kinetics (220 M(-1) s(-1) at pH 7.0 and 25 degrees C). Alternatively, compound III is also formed by dioxygen binding to ferrous LPO at an apparent bimolecular rate constant of (1.8+/-0.2) x 10(5) M(-1) s(-1). Dioxygen binding is reversible and at pH 7.0 the dissociation constant (K(D)) of the oxyferrous form is 6 microM. The rate constant of dioxygen dissociation from compound III is higher than conversion of compound III to ferric LPO, which is not affected by the oxygen concentration and follows a biphasic kinetics. A reaction cycle including the redox intermediates compound II, compound III, and ferrous LPO is proposed, which explains the observed (pseudo-)catalase activity of LPO in the absence of one-electron donors. The relevance of these findings in LPO catalysis is discussed.
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Affiliation(s)
- Walter Jantschko
- Division of Biochemistry, Department of Chemistry, Metalloprotein Research Group, BOKU--University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria
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