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Williams SM, Chatterji D. Dps Functions as a Key Player in Bacterial Iron Homeostasis. ACS OMEGA 2023; 8:34299-34309. [PMID: 37779979 PMCID: PMC10536872 DOI: 10.1021/acsomega.3c03277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Accepted: 08/24/2023] [Indexed: 10/03/2023]
Abstract
Iron plays a vital role in the maintenance of life, being central to various cellular processes, from respiration to gene regulation. It is essential for iron to be stored in a nontoxic and readily available form. DNA binding proteins under starvation (Dps) belong to the ferritin family of iron storage proteins and are adept at storing iron in their hollow protein shells. Existing solely in prokaryotes, these proteins have the additional functions of DNA binding and protection from oxidative stress. Iron storage proteins play a functional role in storage, release, and transfer of iron and therefore are central to the optimal functioning of iron homeostasis. Here we review the multifarious properties of Dps through relevant biochemical and structural studies with a focus on iron storage and ferroxidation. We also examine the role of Dps as a possible candidate as an iron donor to iron-sulfur (Fe-S) clusters, which are ubiquitous to many biological processes.
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Affiliation(s)
- Sunanda Margrett Williams
- Institute
of Structural and Molecular Biology, Birkbeck,
University of London, Malet Street, London WC1E
7HX, United Kingdom
| | - Dipankar Chatterji
- Molecular
Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
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2
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Mohanty A, Parida A, Subhadarshanee B, Behera N, Subudhi T, Koochana PK, Behera RK. Alteration of Coaxial Heme Ligands Reveals the Role of Heme in Bacterioferritin from Mycobacterium tuberculosis. Inorg Chem 2021; 60:16937-16952. [PMID: 34695354 DOI: 10.1021/acs.inorgchem.1c01554] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The uptake and utilization of iron remains critical for the survival/virulence of the host/pathogens in spite of the limitations (low bioavailability/high toxicity) associated with this nutrient. Both the host and pathogens manage to overcome these problems by utilizing the iron repository protein nanocages, ferritins, which not only sequester and detoxify the free Fe(II) ions but also decrease the iron solubility gap by synthesizing/encapsulating the Fe(III)-oxyhydroxide biomineral in its central hollow nanocavity. Bacterial pathogens including Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, encode a distinct subclass of ferritins called bacterioferritin (BfrA), which binds heme, the versatile redox cofactor, via coaxial, conserved methionine (M52) residues at its subunit-dimer interfaces. However, the exact role of heme in Mtb BfrA remains yet to be established. Therefore, its coaxial ligands were altered via site-directed mutagenesis, which resulted in both heme-bound (M52C; ∼1 heme per cage) and heme-free (M52H and M52L) variants, indicating the importance of M52 residues as preferential heme binding axial ligands in Mtb BfrA. All these variants formed intact nanocages of similar size and iron-loading ability as that of wild-type (WT) Mtb BfrA. However, the as-isolated heme-bound variants (WT and M52C) exhibited enhanced protein stability and reductive iron mobilization as compared to their heme-free analogues (M52H and M52L). Further, increasing the heme content in BfrA variants by reconstitution not only enhanced the cage stability but also facilitated the iron mobilization, suggesting the role of heme. In contrary, heme altered the ferroxidase activity to a lesser extent despite facilitating the accumulation of the reactive intermediates formed during the course of the reaction. The current study suggests that heme in Mtb BfrA enhances the overall stability of the protein and possibly acts as an intrinsic electron relay station to influence the iron mineral dissolution and thus may be associated with Mtb's pathogenicity.
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Affiliation(s)
- Abhinav Mohanty
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | - Akankshika Parida
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | | | - Narmada Behera
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | - Tanaya Subudhi
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | | | - Rabindra K Behera
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
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3
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Coleman RE, Boulton RB, Stuchebrukhov AA. Kinetics of autoxidation of tartaric acid in presence of iron. J Chem Phys 2020; 153:064503. [PMID: 35287462 DOI: 10.1063/5.0013727] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The kinetics of the autoxidation reaction of tartaric acid in an air-saturated solution in the presence of Fe(II) show autocatalytic behavior with distinct initiation, propagation, and termination phases. The initiation phase, which involves activation of dissolved oxygen, decreases with increasing pH, over the test range of pH of 2.5-4.5, indicating that activation of oxygen is catalyzed by an Fe(II)-tartrate complex. The autocatalytic nature of this reaction indicates the presence of a catalytic intermediate that is produced during the initiation phase and regenerated during the propagation phase. The addition of catalase, as well as direct measurements, provided evidence of the presence and kinetic action of hydrogen peroxide as one of the intermediates. Direct addition of hydrogen peroxide resulted in shortening of the initiation stage and the propagation phase with similar rates as in the autoxidation reaction at low pH. The propagation is approximately a zero order reaction with respect to oxygen and iron. The kinetic analysis suggests that an intermediate catalytic complex(s) involving a ferryl ion (FeO2+) controls the rate of the propagation reaction. The Fe(III) formation shows autocatalytic behavior that mirrors the dissolved oxygen consumption patterns under all pH conditions studied. At pH values of 2.5 and 3.0, Fe(III) accumulated to a maximum, before it was partially consumed. This maximum coincided with the depletion of dissolved oxygen. The consumption of Fe(III), or the reduction of Fe(III) back to Fe(II), reflects the catalytic nature of Fe(II) and the essential role of tartaric acid in the initiation phase of Fenton's original reaction.
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Affiliation(s)
- Robert E Coleman
- Department of Viticulture and Enology, University of California, Davis, California 95616, USA
| | - Roger B Boulton
- Department of Viticulture and Enology, University of California, Davis, California 95616, USA
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Mohanty A, Subhadarshanee B, Barman P, Mahapatra C, Aishwarya B, Behera RK. Iron Mineralizing Bacterioferritin A from Mycobacterium tuberculosis Exhibits Unique Catalase-Dps-like Dual Activities. Inorg Chem 2019; 58:4741-4752. [DOI: 10.1021/acs.inorgchem.8b02758] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Abhinav Mohanty
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | - Biswamaitree Subhadarshanee
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
- School of Biotechnology, Kalinga Institute of Industrial Technology (KIIT), Bhubaneswar 751024, Odisha, India
| | - Pallavi Barman
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | - Chinmayee Mahapatra
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | - B. Aishwarya
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
| | - Rabindra K. Behera
- Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
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5
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Mehlenbacher M, Poli M, Arosio P, Santambrogio P, Levi S, Chasteen ND, Bou-Abdallah F. Iron Oxidation and Core Formation in Recombinant Heteropolymeric Human Ferritins. Biochemistry 2017. [PMID: 28636371 DOI: 10.1021/acs.biochem.7b00024] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In animals, the iron storage and detoxification protein, ferritin, is composed of two functionally and genetically distinct subunit types, H (heavy) and L (light), which co-assemble in various ratios with tissue specific distributions to form shell-like protein structures of 24 subunits within which a mineralized iron core is stored. The H-subunit possesses a ferroxidase center (FC) that catalyzes Fe(II) oxidation, whereas the L-subunit does not. To assess the role of the L-subunit in iron oxidation and core formation, two human recombinant heteropolymeric ferritins, designated H-rich and L-rich with ratios of ∼20H:4L and ∼22L:2H, respectively, were employed and compared to the human homopolymeric H-subunit ferritin (HuHF). These heteropolymeric ferritins have a composition similar to the composition of those found in hearts and brains (i.e., H-rich) and in livers and spleens (i.e., L-rich). As for HuHF, iron oxidation in H-rich ferritin was found to proceed with a 2:1 Fe(II):O2 stoichiometry at an iron level of 2 Fe(II) atoms/H-subunit with the generation of H2O2. The H2O2 reacted with additional Fe(II) in a 2:1 Fe(II):H2O2 ratio, thus avoiding the production of hydroxyl radical. A μ-1,2-peroxo-diFe(III) intermediate was observed at the FC of H-rich ferritin as for HuHF. Importantly, the H-rich protein regenerated full ferroxidase activity more rapidly than HuHF did and additionally formed larger iron cores, indicating dual roles for the L-subunit in facilitating iron turnover at the FC and in mineralization of the core. The L-rich ferritin, while also facilitating iron oxidation at the FC, additionally promoted oxidation at the mineral surface once the iron binding capacity of the FC was exceeded.
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Affiliation(s)
- Matthew Mehlenbacher
- Department of Chemistry, State University of New York , Potsdam, New York 13676, United States
| | - Maura Poli
- Department of Molecular and Translational Medicine, University of Brescia , 25121 Brescia, Italy
| | - Paolo Arosio
- Department of Molecular and Translational Medicine, University of Brescia , 25121 Brescia, Italy
| | | | | | - N Dennis Chasteen
- Department of Chemistry, University of New Hampshire , Durham, New Hampshire 03824, United States
| | - Fadi Bou-Abdallah
- Department of Chemistry, State University of New York , Potsdam, New York 13676, United States
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Bou-Abdallah F, Yang H, Awomolo A, Cooper B, Woodhall MR, Andrews SC, Chasteen ND. Functionality of the three-site ferroxidase center of Escherichia coli bacterial ferritin (EcFtnA). Biochemistry 2014; 53:483-95. [PMID: 24380371 DOI: 10.1021/bi401517f] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
At least three ferritins are found in the bacterium Escherichia coli : the heme-containing bacterioferritin (EcBFR) and two nonheme bacterial ferritins (EcFtnA and EcFtnB). In addition to the conserved A and B sites of the diiron ferroxidase center, EcFtnA has a third iron-binding site (the C site) of unknown function that is nearby the diiron site. In the present work, the complex chemistry of iron oxidation and deposition in EcFtnA was further defined through a combination of oximetry, pH stat, stopped-flow and conventional kinetics, UV-vis, fluorescence, and EPR spectroscopic measurements on both the wild-type protein and site-directed variants of the A, B, and C sites. The data reveal that although H2O2 is a product of dioxygen reduction in EcFtnA and oxidation occurs with a stoichiometry of Fe(2+)/O2 ∼ 3:1 most of the H2O2 produced is consumed in subsequent reactions with a 2:1 Fe(2+)/H2O2 stoichiometry, thus suppressing hydroxyl-radical formation. Although the A and B sites are essential for rapid iron oxidation, the C site slows oxidation and suppresses iron turnover at the ferroxidase center. A tyrosyl radical, assigned to Tyr24 near the ferroxidase center, is formed during iron oxidation, and its possible significance to the function of the protein is discussed. Taken as a whole, the data indicate that there are multiple iron-oxidation pathways in EcFtnA with O2 and H2O2 as oxidants. Furthermore, our data do not support a universal mechanism for iron oxidation in all ferritins whereby the C site acts as transit site, as has been recently proposed.
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Affiliation(s)
- F Bou-Abdallah
- Department of Chemistry, State University of New York , Potsdam, New York 13676, United States
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The characterization of Thermotoga maritima ferritin reveals an unusual subunit dissociation behavior and efficient DNA protection from iron-mediated oxidative stress. Extremophiles 2011; 15:431-9. [DOI: 10.1007/s00792-011-0374-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Accepted: 03/31/2011] [Indexed: 11/26/2022]
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8
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The iron redox and hydrolysis chemistry of the ferritins. Biochim Biophys Acta Gen Subj 2010; 1800:719-31. [DOI: 10.1016/j.bbagen.2010.03.021] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 03/23/2010] [Accepted: 03/26/2010] [Indexed: 12/12/2022]
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Weeratunga SK, Lovell S, Yao H, Battaile KP, Fischer CJ, Gee CE, Rivera M. Structural studies of bacterioferritin B from Pseudomonas aeruginosa suggest a gating mechanism for iron uptake via the ferroxidase center . Biochemistry 2010; 49:1160-75. [PMID: 20067302 DOI: 10.1021/bi9015204] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The structure of recombinant Pseudomonas aeruginosa bacterioferritin B (Pa BfrB) has been determined from crystals grown from protein devoid of core mineral iron (as-isolated) and from protein mineralized with approximately 600 iron atoms (mineralized). Structures were also obtained from crystals grown from mineralized BfrB after they had been soaked in an FeSO(4) solution (Fe soak) and in separate experiments after they had been soaked in an FeSO(4) solution followed by a soak in a crystallization solution (double soak). Although the structures consist of a typical bacterioferritin fold comprised of a nearly spherical 24-mer assembly that binds 12 heme molecules, comparison of microenvironments observed in the distinct structures provided interesting insights. The ferroxidase center in the as-isolated, mineralized, and double-soak structures is empty. The ferroxidase ligands (except His130) are poised to bind iron with minimal conformational changes. The His130 side chain, on the other hand, must rotate toward the ferroxidase center to coordinate iron. In comparison, the structure obtained from crystals soaked in an FeSO(4) solution displays a fully occupied ferroxidase center and iron bound to the internal, Fe((in)), and external, Fe((out)), surfaces of Pa BfrB. The conformation of His130 in this structure is rotated toward the ferroxidase center and coordinates an iron ion. The structures also revealed a pore on the surface of Pa BfrB that likely serves as a port of entry for Fe(2+) to the ferroxidase center. On its opposite end, the pore is capped by the side chain of His130 when it adopts its "gate-closed" conformation that enables coordination to a ferroxidase iron. A change to its "gate-open", noncoordinative conformation creates a path for the translocation of iron from the ferroxidase center to the interior cavity. These structural observations, together with findings obtained from iron incorporation measurements in solution, suggest that the ferroxidase pore is the dominant entry route for the uptake of iron by Pa BfrB. These findings, which are clearly distinct from those made with Escherichia coli Bfr [Crow, A. C., Lawson, T. L., Lewin, A., Moore, G. R., and Le Brun, N. E. (2009) J. Am. Chem. Soc. 131, 6808-6813], indicate that not all bacterioferritins operate in the same manner.
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Affiliation(s)
- Saroja K Weeratunga
- Ralph N. Adams Institute for Bioanalytical Chemistry and Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Drive, Room 220 E, Lawrence, Kansas 66047, USA
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10
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Chiancone E, Ceci P. The multifaceted capacity of Dps proteins to combat bacterial stress conditions: Detoxification of iron and hydrogen peroxide and DNA binding. Biochim Biophys Acta Gen Subj 2010; 1800:798-805. [PMID: 20138126 DOI: 10.1016/j.bbagen.2010.01.013] [Citation(s) in RCA: 165] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2009] [Revised: 01/25/2010] [Accepted: 01/28/2010] [Indexed: 12/26/2022]
Abstract
BACKGROUND The widely expressed Dps proteins, so named after the DNA-binding properties of the first characterized member of the family in Escherichia coli, are considered major players in the bacterial response to stress. SCOPE OF REVIEW The review describes the distinctive features of the "ferritin-like" ferroxidation reaction, which uses hydrogen peroxide as physiological iron oxidant and therefore permits the concomitant removal of the two reactants that give rise to hydroxyl radicals via Fenton chemistry. It also illustrates the structural elements identified to date that render the interaction of some Dps proteins with DNA possible and outlines briefly the significance of Dps-DNA complex formation and of the Dps interaction with other DNA-binding proteins in relation to the organization of the nucleoid and microbial survival. GENERAL SIGNIFICANCE Understanding in molecular terms the distinctive role of Dps proteins in bacterial resistance to general and specific stress conditions. MAJOR CONCLUSIONS The state of the art is that the response to oxidative and peroxide-mediated stress is mediated directly by Dps proteins via their ferritin-like activity. In contrast, the response to other stress conditions derives from the concerted interplay of diverse interactions that Dps proteins may establish with DNA and with other DNA-binding proteins.
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Affiliation(s)
- Emilia Chiancone
- Department of Biochemical Sciences 'A. Rossi Fanelli', "Sapienza" University of Rome, Rome, Italy.
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Zhang B, Watt GD. Anaerobic iron deposition into horse spleen, recombinant human heavy and light and bacteria ferritins by large oxidants. J Inorg Biochem 2007; 101:1676-85. [PMID: 17804076 DOI: 10.1016/j.jinorgbio.2007.06.043] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Revised: 06/22/2007] [Accepted: 06/28/2007] [Indexed: 11/17/2022]
Abstract
Large-molecule oxidants oxidize Fe(II) to form Fe(III) cores in the interior of ferritins at rates comparable to or faster than the iron deposition reaction using O(2) as oxidant. Iron deposition into horse spleen ferritin (HoSF) occurs using ferricyanide ion, 2,6-dichlorophenol-indophenol, and several redox proteins: cytochrome c, stellacyanin, and ceruloplasmin. Cytochrome c also loads iron into recombinant human H-chain (rHF), human L-chain (rLF), and A. vinelandii bacterioferritin (AvBF). The enzymatic activities of ferritins were monitored anaerobically using stopped-flow kinetic spectrophotometry. The reactions exhibit saturation kinetics with respect to the large oxidant concentrations, giving apparent Michaelis constants for cytochrome c as oxidant: K(m)=39.6 microM for HoSF and 6.9 microM for AvBF. Comparison of the kinetic parameters with that of iron deposition by O(2) shows that large oxidants load iron into HoSF and AvBF more effectively than O(2) and may use a mechanism different than the ferroxidase center. Large oxidants did not deposit iron as efficiently with rHF and rLF. The results suggest that the heme groups in AvBF and the protein redox centers present in heteropolymers may assist in anaerobic iron deposition by large oxidants. The physiological relevance of iron deposition by large molecules, including protein oxidants is discussed.
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Affiliation(s)
- Bo Zhang
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA
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Bou-Abdallah F, Carney E, Chasteen ND, Arosio P, Viescas AJ, Papaefthymiou GC. A comparative Mössbauer study of the mineral cores of human H-chain ferritin employing dioxygen and hydrogen peroxide as iron oxidants. Biophys Chem 2007; 130:114-21. [PMID: 17881115 PMCID: PMC2156192 DOI: 10.1016/j.bpc.2007.08.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Accepted: 08/04/2007] [Indexed: 11/20/2022]
Abstract
Ferritins are ubiquitous iron storage and detoxification proteins distributed throughout the plant and animal kingdoms. Mammalian ferritins oxidize and accumulate iron as a ferrihydrite mineral within a shell-like protein cavity. Iron deposition utilizes both O(2) and H(2)O(2) as oxidants for Fe(2+) where oxidation can occur either at protein ferroxidase centers or directly on the surface of the growing mineral core. The present study was undertaken to determine whether the nature of the mineral core formed depends on the protein ferroxidase center versus mineral surface mechanism and on H(2)O(2) versus O(2) as the oxidant. The data reveal that similar cores are produced in all instances, suggesting that the structure of the core is thermodynamically, not kinetically controlled. Cores averaging 500 Fe/protein shell and diameter approximately 2.6 nm were prepared and exhibited superparamagnetic blocking temperatures of 19 and 22 K for the H(2)O(2) and O(2) oxidized samples, respectively. The observed blocking temperatures are consistent with the unexpectedly large effective anisotropy constant K(eff)=312 kJ/m(3) recently reported for ferrihydrite nanoparticles formed in reverse micelles [E.L. Duarte, R. Itri, E. Lima Jr., M.S. Batista, T.S. Berquó and G.F. Goya, Large Magnetic Anisotropy in ferrihydrite nanoparticles synthesized from reverse micelles, Nanotechnology 17 (2006) 5549-5555.]. All ferritin samples exhibited two magnetic phases present in nearly equal amounts and ascribed to iron spins at the surface and in the interior of the nanoparticle. At 4.2 K, the surface spins exhibit hyperfine fields, H(hf), of 436 and 445 kOe for the H(2)O(2) and O(2) samples, respectively. As expected, the spins in the interior of the core exhibit larger H(hf) values, i.e. 478 and 486 kOe for the H(2)O(2) and O(2) samples, respectively. The slightly smaller hyperfine field distribution DH(hf) for both surface (78 kOe vs. 92 kOe) and interior spins (45 kOe vs. 54 kOe) of the O(2) sample compared to the H(2)O(2) samples implies that the former is somewhat more crystalline.
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Affiliation(s)
- Fadi Bou-Abdallah
- Department of Chemistry, University of New Hampshire, Durham, NH 03824, USA
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Zhang B, Wilson PE, Watt GD. Ferritin-catalyzed consumption of hydrogen peroxide by amine buffers causes the variable Fe2+ to O2 stoichiometry of iron deposition in horse spleen ferritin. J Biol Inorg Chem 2006; 11:1075-86. [PMID: 16896807 DOI: 10.1007/s00775-006-0141-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Accepted: 06/27/2006] [Indexed: 11/24/2022]
Abstract
Ferritin catalyzes the oxidation of Fe2+ by O2 to form a reconstituted Fe3+ oxy-hydroxide mineral core, but extensive studies have shown that the Fe2+ to O2 stoichiometry changes with experimental conditions. At Fe2+ to horse spleen ferritin (HoSF) ratios greater than 200, an upper limit of Fe2+ to O2 of 4 is typically measured, indicating O2 is reduced to 2H2O. In contrast, a lower limit of Fe2+ to O2 of approximately 2 is measured at low Fe2+ to HoSF ratios, implicating H2O2 as a product of Fe2+ deposition. Stoichiometric amounts of H2O2 have not been measured, and H2O2 is proposed to react with an unknown system component. Evidence is presented that identifies this component as amine buffers, including 3-N-morpholinopropanesulfonic acid (MOPS), which is widely used in ferritin studies. In the presence of non-amine buffers, the Fe2+ to O2 stoichiometry was approximately 4.0, but at high concentrations of amine buffers (0.10 M) the Fe2+ to O2 stoichiometry is approximately 2.5 for iron loadings of eight to 30 Fe2+ per HoSF. Decreasing the concentration of amine buffer to zero resulted in an Fe2+ to O2 stoichiometry of approximately 4. Direct evidence for amine buffer modification during Fe2+ deposition was obtained by comparing authentic and modified buffers using mass spectrometry, NMR, and thin layer chromatography. Tris(hydroxymethyl)aminomethane, MOPS, and N-methylmorpholine (a MOPS analog) were all rapidly chemically modified during Fe2+ deposition to form N-oxides. Under identical conditions no modification was detected when amine buffer, H2O2, and O2 were combined with Fe2+ or ferritin separately. Thus, a short-lived ferritin intermediate is required for buffer modification by H2O2. Variation of the Fe2+ to O2 stoichiometry versus the Fe2+ to HoSF ratio and the amine buffer concentration are consistent with buffer modification.
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Affiliation(s)
- Bo Zhang
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA
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14
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Zhao G, Chasteen ND. Oxidation of Good’s buffers by hydrogen peroxide. Anal Biochem 2006; 349:262-7. [PMID: 16289439 DOI: 10.1016/j.ab.2005.10.005] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Revised: 09/30/2005] [Accepted: 10/04/2005] [Indexed: 11/17/2022]
Abstract
Good's zwitterionic buffers are widely used in biological and biochemical research in which hydrogen peroxide is a solution component. This study was undertaken to determine whether Good's buffers exhibit reactivity toward H(2)O(2). It is found that H(2)O(2) oxidizes both morpholine ring-containing buffers (e.g., Mops, Mes) and piperazine ring-containing zwitterionic buffers (e.g., Pipes, Hepes, and Epps) to produce their corresponding N-oxide forms. The percentage of oxidized buffer increases as the concentration of H(2)O(2) increases. However, the rate of oxidation is relatively slow. For example, no oxidized Mops was detected 2h after adding 0.1M H(2)O(2) to 0.1M Mops (pH 7.0), and only 5.7% was oxidized after 24h exposure to H(2)O(2). Thus, although all of these buffers can be oxidized by H(2)O(2), their slow reaction does not significantly perturb levels of H(2)O(2) in the time frame and at the concentrations of most biochemical studies. Therefore, the previously reported rapid loss of H(2)O(2) produced from the ferroxidase reaction of ferritin is unlikely due to reaction of H(2)O(2) with buffer, a conclusion supported by the fact that H(2)O(2) is also lost rapidly when the solution pH of the ferroxidase reaction is controlled by a pH stat apparatus in the absence of buffer.
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Affiliation(s)
- Guanghua Zhao
- Department of Chemistry, University of New Hampshire, Durham, NH 03824, USA
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