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Niks D, Hille R. Molybdenum- and tungsten-containing formate dehydrogenases and formylmethanofuran dehydrogenases: Structure, mechanism, and cofactor insertion. Protein Sci 2019; 28:111-122. [PMID: 30120799 PMCID: PMC6295890 DOI: 10.1002/pro.3498] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 08/10/2018] [Accepted: 08/13/2018] [Indexed: 12/20/2022]
Abstract
An overview is provided of the molybdenum- and tungsten-containing enzymes that catalyze the interconversion of formate and CO2 , focusing on common structural and mechanistic themes, as well as a consideration of the manner in which the mature Mo- or W-containing cofactor is inserted into apoprotein.
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Abstract
Two factors, climate change brought on by rising atmospheric CO2 levels and the accelerating shift toward renewable energy sources, have together worked to heighten interest in understanding how biological catalysts so effectively bring about the reduction of CO2 to formate, with potential applications for both bioremediation and energy storage. Most metal-dependent formate dehydrogenases, containing either molybdenum or tungsten in their active sites, function physiologically in the direction of formate oxidation to CO2, but it has become clear that many, if not all, are also effective in catalyzing the reverse reaction. In this chapter, we describe methods for isolating and characterizing these enzymes.
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Peters JW, Beratan DN, Bothner B, Dyer RB, Harwood CS, Heiden ZM, Hille R, Jones AK, King PW, Lu Y, Lubner CE, Minteer SD, Mulder DW, Raugei S, Schut GJ, Seefeldt LC, Tokmina-Lukaszewska M, Zadvornyy OA, Zhang P, Adams MW. A new era for electron bifurcation. Curr Opin Chem Biol 2018; 47:32-38. [PMID: 30077080 DOI: 10.1016/j.cbpa.2018.07.026] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 06/16/2018] [Accepted: 07/18/2018] [Indexed: 11/17/2022]
Abstract
Electron bifurcation, or the coupling of exergonic and endergonic oxidation-reduction reactions, was discovered by Peter Mitchell and provides an elegant mechanism to rationalize and understand the logic that underpins the Q cycle of the respiratory chain. Thought to be a unique reaction of respiratory complex III for nearly 40 years, about a decade ago Wolfgang Buckel and Rudolf Thauer discovered that flavin-based electron bifurcation is also an important component of anaerobic microbial metabolism. Their discovery spawned a surge of research activity, providing a basis to understand flavin-based bifurcation, forging fundamental parallels with Mitchell's Q cycle and leading to the proposal of metal-based bifurcating enzymes. New insights into the mechanism of electron bifurcation provide a foundation to establish the unifying principles and essential elements of this fascinating biochemical phenomenon.
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Watson C, Niks D, Hille R, Vieira M, Schoepp-Cothenet B, Marques AT, Romão MJ, Santos-Silva T, Santini JM. Electron transfer through arsenite oxidase: Insights into Rieske interaction with cytochrome c. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2017; 1858:865-872. [PMID: 28801050 PMCID: PMC5574378 DOI: 10.1016/j.bbabio.2017.08.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Revised: 07/05/2017] [Accepted: 08/05/2017] [Indexed: 11/25/2022]
Abstract
Arsenic is a widely distributed environmental toxin whose presence in drinking water poses a threat to >140 million people worldwide. The respiratory enzyme arsenite oxidase from various bacteria catalyses the oxidation of arsenite to arsenate and is being developed as a biosensor for arsenite. The arsenite oxidase from Rhizobium sp. str. NT-26 (a member of the Alphaproteobacteria) is a heterotetramer consisting of a large catalytic subunit (AioA), which contains a molybdenum centre and a 3Fe-4S cluster, and a small subunit (AioB) containing a Rieske 2Fe-2S cluster. Stopped-flow spectroscopy and isothermal titration calorimetry (ITC) have been used to better understand electron transfer through the redox-active centres of the enzyme, which is essential for biosensor development. Results show that oxidation of arsenite at the active site is extremely fast with a rate of >4000s-1 and reduction of the electron acceptor is rate-limiting. An AioB-F108A mutation results in increased activity with the artificial electron acceptor DCPIP and decreased activity with cytochrome c, which in the latter as demonstrated by ITC is not due to an effect on the protein-protein interaction but instead to an effect on electron transfer. These results provide further support that the AioB F108 is important in electron transfer between the Rieske subunit and cytochrome c and its absence in the arsenite oxidases from the Betaproteobacteria may explain the inability of these enzymes to use this electron acceptor.
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Yu X, Niks D, Mulchandani A, Hille R. Efficient reduction of CO 2 by the molybdenum-containing formate dehydrogenase from Cupriavidus necator ( Ralstonia eutropha). J Biol Chem 2017; 292:16872-16879. [PMID: 28784661 DOI: 10.1074/jbc.m117.785576] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 08/03/2017] [Indexed: 11/06/2022] Open
Abstract
The ability of the FdsABG formate dehydrogenase from Cupriavidus necator (formerly known as Ralstonia eutropha) to catalyze the reverse of the physiological reaction, the reduction of CO2 to formate utilizing NADH as electron donor, has been investigated. Contrary to previous studies of this enzyme, we demonstrate that it is in fact effective in catalyzing the reverse reaction with a kcat of 11 ± 0.4 s-1 We also quantify the stoichiometric accumulation of formic acid as the product of the reaction and demonstrate that the observed kinetic parameters for catalysis in the forward and reverse reactions are thermodynamically consistent, complying with the expected Haldane relationships. Finally, we demonstrate the reaction conditions necessary for gauging the ability of a given formate dehydrogenase or other CO2-utilizing enzyme to catalyze the reverse direction to avoid false negative results. In conjunction with our earlier studies on the reaction mechanism of this enzyme and on the basis of the present work, we conclude that all molybdenum- and tungsten-containing formate dehydrogenases and related enzymes likely operate via a simple hydride transfer mechanism and are effective in catalyzing the reversible interconversion of CO2 and formate under the appropriate experimental conditions.
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Dingwall S, Wilcoxen J, Niks D, Hille R. Studies of carbon monoxide dehydrogenase from Oligotropha carboxidovorans. ACTA ACUST UNITED AC 2016. [DOI: 10.1016/j.molcatb.2016.10.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Niks D, Duvvuru J, Escalona M, Hille R. Spectroscopic and Kinetic Properties of the Molybdenum-containing, NAD+-dependent Formate Dehydrogenase from Ralstonia eutropha. J Biol Chem 2015; 291:1162-74. [PMID: 26553877 DOI: 10.1074/jbc.m115.688457] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Indexed: 11/06/2022] Open
Abstract
We have examined the rapid reaction kinetics and spectroscopic properties of the molybdenum-containing, NAD(+)-dependent FdsABG formate dehydrogenase from Ralstonia eutropha. We confirm previous steady-state studies of the enzyme and extend its characterization to a rapid kinetic study of the reductive half-reaction (the reaction of formate with oxidized enzyme). We have also characterized the electron paramagnetic resonance signal of the molybdenum center in its Mo(V) state and demonstrated the direct transfer of the substrate Cα hydrogen to the molybdenum center in the course of the reaction. Varying temperature, microwave power, and level of enzyme reduction, we are able to clearly identify the electron paramagnetic resonance signals for four of the iron/sulfur clusters of the enzyme and find suggestive evidence for two others; we observe a magnetic interaction between the molybdenum center and one of the iron/sulfur centers, permitting assignment of this signal to a specific iron/sulfur cluster in the enzyme. In light of recent advances in our understanding of the structure of the molybdenum center, we propose a reaction mechanism involving direct hydride transfer from formate to a molybdenum-sulfur group of the molybdenum center.
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Wang J, Krizowski S, Fischer-Schrader K, Niks D, Tejero J, Sparacino-Watkins C, Wang L, Ragireddy V, Frizzell S, Kelley EE, Zhang Y, Basu P, Hille R, Schwarz G, Gladwin MT. Sulfite Oxidase Catalyzes Single-Electron Transfer at Molybdenum Domain to Reduce Nitrite to Nitric Oxide. Antioxid Redox Signal 2015; 23:283-94. [PMID: 25314640 PMCID: PMC4523048 DOI: 10.1089/ars.2013.5397] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
AIMS Recent studies suggest that the molybdenum enzymes xanthine oxidase, aldehyde oxidase, and mARC exhibit nitrite reductase activity at low oxygen pressures. However, inhibition studies of xanthine oxidase in humans have failed to block nitrite-dependent changes in blood flow, leading to continued exploration for other candidate nitrite reductases. Another physiologically important molybdenum enzyme—sulfite oxidase (SO)—has not been extensively studied. RESULTS Using gas-phase nitric oxide (NO) detection and physiological concentrations of nitrite, SO functions as nitrite reductase in the presence of a one-electron donor, exhibiting redox coupling of substrate oxidation and nitrite reduction to form NO. With sulfite, the physiological substrate, SO only facilitates one turnover of nitrite reduction. Studies with recombinant heme and molybdenum domains of SO indicate that nitrite reduction occurs at the molybdenum center via coupled oxidation of Mo(IV) to Mo(V). Reaction rates of nitrite to NO decreased in the presence of a functional heme domain, mediated by steric and redox effects of this domain. Using knockdown of all molybdopterin enzymes and SO in fibroblasts isolated from patients with genetic deficiencies of molybdenum cofactor and SO, respectively, SO was found to significantly contribute to hypoxic nitrite signaling as demonstrated by activation of the canonical NO-sGC-cGMP pathway. INNOVATION Nitrite binds to and is reduced at the molybdenum site of mammalian SO, which may be allosterically regulated by heme and molybdenum domain interactions, and contributes to the mammalian nitrate-nitrite-NO signaling pathway in human fibroblasts. CONCLUSION SO is a putative mammalian nitrite reductase, catalyzing nitrite reduction at the Mo(IV) center.
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Hall J, Reschke S, Cao H, Leimkühler S, Hille R. The reductive half-reaction of xanthine dehydrogenase from Rhodobacter capsulatus: the role of Glu232 in catalysis. J Biol Chem 2014; 289:32121-32130. [PMID: 25258317 DOI: 10.1074/jbc.m114.603456] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The kinetic properties of an E232Q variant of the xanthine dehydrogenase from Rhodobacter capsulatus have been examined to ascertain whether Glu(232) in wild-type enzyme is protonated or unprotonated in the course of catalysis at neutral pH. We find that kred, the limiting rate constant for reduction at high [xanthine], is significantly compromised in the variant, a result that is inconsistent with Glu(232) being neutral in the active site of the wild-type enzyme. A comparison of the pH dependence of both kred and kred/Kd from reductive half-reaction experiments between wild-type and enzyme and the E232Q variant suggests that the ionized Glu(232) of wild-type enzyme plays an important role in catalysis by discriminating against the monoanionic form of substrate, effectively increasing the pKa of substrate by two pH units and ensuring that at physiological pH the neutral form of substrate predominates in the Michaelis complex. A kinetic isotope study of the wild-type R. capsulatus enzyme indicates that, as previously determined for the bovine and chicken enzymes, product release is principally rate-limiting in catalysis. The disparity in rate constants for the chemical step of the reaction and product release, however, is not as great in the bacterial enzyme as compared with the vertebrate forms. The results indicate that the bacterial and bovine enzymes catalyze the chemical step of the reaction to the same degree and that the faster turnover observed with the bacterial enzyme is due to a faster rate constant for product release than is seen with the vertebrate enzyme.
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Schwarz G, Krizowski S, Wang J, Niks D, Sparacino-Watkins C, Hille R, Gladwin M. Intramolecular electron transfer controls nitrite reduction in molybdenum-containing sulfite oxidase. Nitric Oxide 2014. [DOI: 10.1016/j.niox.2014.09.045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Lee MCI, Velayutham M, Komatsu T, Hille R, Zweier JL. Measurement and characterization of superoxide generation from xanthine dehydrogenase: a redox-regulated pathway of radical generation in ischemic tissues. Biochemistry 2014; 53:6615-23. [PMID: 25243829 PMCID: PMC4204892 DOI: 10.1021/bi500582r] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The enzyme xanthine oxidoreductase
(XOR) is an important source
of oxygen free radicals and related postischemic injury. Xanthine
dehydrogenase (XDH), the major form of XOR in tissues, can be converted
to xanthine oxidase (XO) by oxidation of sulfhydryl residues or by
proteolysis. The conversion of XDH to XO has been assumed to be required
for radical generation and tissue injury. It is also possible that
XDH could generate significant quantities of superoxide, •O2–, for cellular signaling or injury;
however, this possibility and its potential ramifications have not
been previously considered. To unambiguously determine if XDH can
be a significant source of •O2–, experiments were performed to measure and characterize •O2– generation using XDH from chicken
liver that is locked in the dehydrogenase conformation. Electron paramagnetic
resonance spin trapping experiments with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide demonstrated that XDH in the presence of xanthine
produces significant amounts of •O2–. NAD+ and NADH inhibited the generation
of •O2– from XDH in
a dose-dependent manner, with NAD+ exhibiting stronger
inhibition than NADH at low physiological concentrations. Decreased
amounts of NAD+ and NADH, which occur during and following
tissue ischemia, enhanced the generation of •O2– from XDH in the presence of xanthine.
It was observed that XDH-mediated oxygen radical generation markedly
depressed Ca2+-ATPase activity of isolated sarcoplasmic
reticulum vesicles from cardiac muscle, and this was modulated by
NAD+ and NADH. Thus, XDH can be an important redox-regulated
source of •O2– generation
in ischemic tissue, and conversion to XO is not required to activate
radical formation and subsequent tissue injury.
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Cao H, Pauff JM, Hille R. X-ray crystal structure of a xanthine oxidase complex with the flavonoid inhibitor quercetin. JOURNAL OF NATURAL PRODUCTS 2014; 77:1693-1699. [PMID: 25060641 DOI: 10.1021/np500320g] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Xanthine oxidase catalyzes the sequential hydroxylation of hypoxanthine to uric acid via xanthine as intermediate. Deposition of crystals of the catalytic product uric acid or its monosodium salt in human joints with accompanying joint inflammation is the major cause of gout. Natural flavonoids are attractive leads for rational design of preventive and therapeutic xanthine oxidase inhibitors due to their beneficial antioxidant, anti-inflammatory, and antiproliferative activities in addition to their micromolar inhibitory activities toward xanthine oxidase. We determined the first complex X-ray structure of mammalian xanthine oxidase with the natural flavonoid inhibitor quercetin at 2.0 Å resolution. The inhibitor adopts a single orientation with its benzopyran moiety sandwiched between Phe 914 and Phe 1009 and ring B pointing toward the solvent channel leading to the molybdenum active center. The favorable steric complementarity of the conjugated three-ring structure of quercetin with the active site and specific hydrogen-bonding interactions of exocyclic hydroxy groups with catalytically relevant residues Arg 880 and Glu 802 correlate well with a previously reported structure-activity relationship of flavonoid inhibitors of xanthine oxidase. The current complex provides a structural basis for the rational design of flavonoid-type inhibitors against xanthine oxidase useful for the treatment of hyperuricemia, gout, and inflammatory disease states.
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Anderson RF, Shinde SS, Hille R, Rothery RA, Weiner JH, Rajagukguk S, Maklashina E, Cecchini G. Electron-transfer pathways in the heme and quinone-binding domain of complex II (succinate dehydrogenase). Biochemistry 2014; 53:1637-46. [PMID: 24559074 PMCID: PMC3985935 DOI: 10.1021/bi401630m] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
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Single electron transfers have been
examined in complex II (succinate:ubiquinone
oxidoreductase) by the method of pulse radiolysis. Electrons are introduced
into the enzyme initially at the [3Fe–4S] and ubiquinone sites
followed by intramolecular equilibration with the b heme of the enzyme. To define thermodynamic and other controlling
parameters for the pathways of electron transfer in complex II, site-directed
variants were constructed and analyzed. Variants at SdhB-His207 and
SdhB-Ile209 exhibit significantly perturbed electron transfer between
the [3Fe–4S] cluster and ubiquinone. Analysis of the data using
Marcus theory shows that the electronic coupling constants for wild-type
and variant enzyme are all small, indicating that electron transfer
occurs by diabatic tunneling. The presence of the ubiquinone is necessary
for efficient electron transfer to the heme, which only slowly equilibrates
with the [3Fe–4S] cluster in the absence of the quinone.
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Cao H, Hall J, Hille R. Substrate orientation and specificity in xanthine oxidase: crystal structures of the enzyme in complex with indole-3-acetaldehyde and guanine. Biochemistry 2014; 53:533-41. [PMID: 24397336 DOI: 10.1021/bi401465u] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Xanthine oxidase is a molybdenum-containing hydroxylase that catalyzes the hydroxylation of sp(2)-hybridized carbon centers in a variety of aromatic heterocycles as well as aldehydes. Crystal structures of the oxidase form of the bovine enzyme in complex with a poor substrate indole-3-acetaldehyde and the nonsubstrate guanine have been determined, both at a resolution of 1.6 Å. In each structure, a specific and unambiguous orientation of the substrate in the active site is observed in which the hydroxylatable site is oriented away from the active site molybdenum center. The orientation seen with indole-3-acetaldehyde has the substrate positioned with the indole ring rather than the exocyclic aldehyde nearest the molybdenum center, indicating that the substrate must rotate some 30° in the enzyme active site to permit hydroxylation of the aldehyde group (as observed experimentally), accounting for the reduced reactivity of the enzyme toward this substrate. The principal product of hydroxylation of indole-3-acetaldehyde by the bovine enzyme is confirmed to be indole-3-carboxylic acid based on its characteristic UV-vis spectrum, and the kinetics of enzyme reduction are reported. With guanine, the dominant orientation seen crystallographically has the C-8 position that might be hydroxylated pointed away from the active site molybdenum center, in a configuration resembling that seen previously with hypoxanthine (a substrate that is effectively hydroxylated at position 2). The ∼180° reorientation required to permit reaction is sterically prohibited, indicating that substrate (mis)orientation in the active site is a major factor precluding formation of the highly mutagenic 8-hydroxyguanine.
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Shanmugam M, Wilcoxen J, Habel-Rodriguez D, Cutsail GE, Kirk ML, Hoffman BM, Hille R. (13)C and (63,65)Cu ENDOR studies of CO dehydrogenase from Oligotropha carboxidovorans. Experimental evidence in support of a copper-carbonyl intermediate. J Am Chem Soc 2013; 135:17775-82. [PMID: 24147852 DOI: 10.1021/ja406136f] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report here an ENDOR study of an S = 1/2 intermediate state trapped during reduction of the binuclear Mo/Cu enzyme CO dehydrogenase by CO. ENDOR spectra of this state confirm that the (63,65)Cu nuclei exhibits strong and almost entirely isotropic coupling to the unpaired electron, show that this coupling atypically has a positive sign, aiso = +148 MHz, and indicate an apparently undetectably small quadrupolar coupling. When the intermediate is generated using (13)CO, coupling to the (13)C is observed, with aiso = +17.3 MHz. A comparison with the couplings seen in related, structurally assigned Mo(V) species from xanthine oxidase, in conjunction with complementary computational studies, leads us to conclude that the intermediate contains a partially reduced Mo(V)/Cu(I) center with CO bound at the copper. Our results provide strong experimental support for a reaction mechanism that proceeds from a comparable complex of CO with fully oxidized Mo(VI)/Cu(I) enzyme.
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Reschke S, Niks D, Wilson H, Sigfridsson KGV, Haumann M, Rajagopalan KV, Hille R, Leimkühler S. Effect of Exchange of the Cysteine Molybdenum Ligand with Selenocysteine on the Structure and Function of the Active Site in Human Sulfite Oxidase. Biochemistry 2013; 52:8295-303. [DOI: 10.1021/bi4008512] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Wilcoxen J, Hille R. The hydrogenase activity of the molybdenum/copper-containing carbon monoxide dehydrogenase of Oligotropha carboxidovorans. J Biol Chem 2013; 288:36052-60. [PMID: 24165123 DOI: 10.1074/jbc.m113.522441] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The reaction of the air-tolerant CO dehydrogenase from Oligotropha carboxidovorans with H2 has been examined. Like the Ni-Fe CO dehydrogenase, the enzyme can be reduced by H2 with a limiting rate constant of 5.3 s(-1) and a dissociation constant Kd of 525 μM; both kred and kred/Kd, reflecting the breakdown of the Michaelis complex and the reaction of free enzyme with free substrate in the low [S] regime, respectively, are largely pH-independent. During the reaction with H2, a new EPR signal arising from the Mo/Cu-containing active site of the enzyme is observed which is distinct from the signal seen when the enzyme is reduced by CO, with greater g anisotropy and larger hyperfine coupling to the active site (63,65)Cu. The signal also exhibits hyperfine coupling to at least two solvent-exchangeable protons of bound substrate that are rapidly exchanged with solvent. Proton coupling is also evident in the EPR signal seen with the dithionite-reduced native enzyme, and this coupling is lost in the presence of bicarbonate. We attribute the coupled protons in the dithionite-reduced enzyme to coordinated water at the copper site in the native enzyme and conclude that bicarbonate is able to displace this water from the copper coordination sphere. On the basis of our results, a mechanism for H2 oxidation is proposed which involves initial binding of H2 to the copper of the binuclear center, displacing the bound water, followed by sequential deprotonation through a copper-hydride intermediate to reduce the binuclear center.
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Appel AM, Bercaw JE, Bocarsly AB, Dobbek H, DuBois DL, Dupuis M, Ferry JG, Fujita E, Hille R, Kenis PJA, Kerfeld CA, Morris RH, Peden CHF, Portis AR, Ragsdale SW, Rauchfuss TB, Reek JNH, Seefeldt LC, Thauer RK, Waldrop GL. Frontiers, opportunities, and challenges in biochemical and chemical catalysis of CO2 fixation. Chem Rev 2013; 113:6621-58. [PMID: 23767781 PMCID: PMC3895110 DOI: 10.1021/cr300463y] [Citation(s) in RCA: 1274] [Impact Index Per Article: 115.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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45
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Brugger N, Krause R, Carlen F, Rimensberger C, Hille R, Steck H, Wilhelm M, Seiler C. Effect of lifetime endurance training on left atrial mechanical function and on the risk of atrial fibrillation. Eur Heart J 2013. [DOI: 10.1093/eurheartj/eht308.1907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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46
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Kümmerle E, Möllmann-Coers M, Pomplun E, Hille R. Fast online system for forecasting environmental impact during an incident. KERNTECHNIK 2013. [DOI: 10.3139/124.100344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Abstract
In an incident, the operational control staff needs a rapid general view of the radiological situation in the vicinity of the emission source which is suitable for decision support. Because the measuring team cannot provide sufficient measurements immediately, model calculations based on the available information about the course of the accident are additionally required. Such calculations do not only serve to create an overview of the current situation but can also provide prognoses for several hours. For this purpose, a software system for environmental impact forecasting was developed at Research Centre Jülich, which calculates time-integrated doses as well as ambient gamma dose rates and activity values. The latter can be directly compared with values measured during the incident and consequently can be used to assess the model assumptions.
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Dederichs H, Pillath J, Lennartz R, Hill P, Hille R. The time-dependent effect of the biological component of 137Cs soil contamination. KERNTECHNIK 2013. [DOI: 10.3139/124.100189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Abstract
In investigations of the long-term development of the population dose in the highly contaminated regions of the Commonwealth of Independence States it was found that the external dose has not decreased as strongly as expected since 1992. Further investigations have shown that, contrary to expectations, no linear correlation can be observed between soil contamination and measured area dose rate. As a contribution towards clarifying these issues, the area dose rate and the soil contamination including the plant fraction were investigated in the Korma district, Belarus. It was found that it is necessary to cover and average over larger areas in order to determine from ground contamination the long-term development of the external dose commitment. This means that for this purpose the introduction of an “effective” surface contamination (sum of mineral and organic contamination components) is necessary. The phenomena observed are described in a model, which permits an analytical calculation of the contamination profile in soil taking migration and transfer effects into account. The differences observed between the measured soil contamination and the resulting external doses or the directly measured dose rate can be explained by the proposed model. Moreover, their long-term development can be calculated. The results show that a time decade after the accident the biological part of the “effective” soil contamination becomes dominant and cannot be neglected.
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48
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Pushie MJ, Cotelesage JJH, Lyashenko G, Hille R, George GN. X-ray Absorption Spectroscopy of a Quantitatively Mo(V) Dimethyl Sulfoxide Reductase Species. Inorg Chem 2013; 52:2830-7. [DOI: 10.1021/ic301660e] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Abstract
A perspective is provided of recent advances in our understanding of molybdenum-containing enzymes other than nitrogenase, a large and diverse group of enzymes that usually (but not always) catalyze oxygen atom transfer to or from a substrate, utilizing a Mo=O group as donor or acceptor. An emphasis is placed on the diversity of protein structure and reaction catalyzed by each of the three major families of these enzymes.
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50
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Lambeck IC, Fischer-Schrader K, Niks D, Roeper J, Chi JC, Hille R, Schwarz G. Molecular mechanism of 14-3-3 protein-mediated inhibition of plant nitrate reductase. J Biol Chem 2011; 287:4562-71. [PMID: 22170050 DOI: 10.1074/jbc.m111.323113] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
14-3-3 proteins regulate key processes in eukaryotic cells including nitrogen assimilation in plants by tuning the activity of nitrate reductase (NR), the first and rate-limiting enzyme in this pathway. The homodimeric NR harbors three cofactors, each of which is bound to separate domains, thus forming an electron transfer chain. 14-3-3 proteins inhibit NR by binding to a conserved phosphorylation site localized in the linker between the heme and molybdenum cofactor-containing domains. Here, we have investigated the molecular mechanism of 14-3-3-mediated NR inhibition using a fragment of the enzyme lacking the third domain, allowing us to analyze electron transfer from the heme cofactor via the molybdenum center to nitrate. The kinetic behavior of the inhibited Mo-heme fragment indicates that the principal point at which 14-3-3 acts is the electron transfer from the heme to the molybdenum cofactor. We demonstrate that this is not due to a perturbation of the reduction potentials of either the heme or the molybdenum center and conclude that 14-3-3 most likely inhibits nitrate reductase by inducing a conformational change that significantly increases the distance between the two redox-active sites.
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