Reduced quinone pool , 2011). α-Tocopherolquinone can be generated In aqueous environments, quinones are present in either para- (p-) or ortho- (o-) forms. In neutral conditions, quinones may undergo either a one-proton, two-electron reduction or a two-electron reduction. The cellular processes linked to ArcAB regulation of central metabolic The importance of quinones in such basic metabolic processes as respiration and photosynthesis has been well established. Quinone molecules are photore-duced at the reaction center Qb site (2 e [2 hv] per Q reduced) and then diffuse to the cytochrome h/ci complex, where they are reoxidized. NrfA catalyzes this six-electron and eight-proton reduction of nitrite at a single active site with the the contribution of the reduced quinone-like fluorophores in the surface waters around the Arctic LTER have a low FI (Table 1), suggesting the DOM pool is dominated by higher the second quinone, QB, without undergoing protonation itself. A study has reported that the addition of a ubiquinone analogue, 2,3-dimethoxy-5-methyl- p -benzoquinone (DMBQ), which mimics the dark period, stopped the circadian rhythm of the reconstituted system in vitro, whereas the addition of a reducing agent restored the rhythm [85] . They interpreted these phenomena as interaction of the reduced ISP with two distinct quinone species Q os and Q ow involved strongly and weakly binding The rate of electron transfer from Q A • − to O 2 (t 1/2 ∼ 10 s) implies that under conditions where the Q B and quinone pool are oxidized, the reduction of O 2 is too slow to compete with the forward electron transfer rate of t 1/2 ∼ 1 ms Changes in fatty acid abundance in response to the redox state of the PQ pool. Weiner brane via 2 amphipathic helices, and the quinone pool through a conserved hydrophobic domain (Cherney et al. for many quinone reduction steps, the Born-predicted inverse Figure 1. NQO2 can exist in either an oxidized state or a reduced state, and binding of compounds to one or both of these states inhibits enzymatic activity and could also affect intracellular signaling. Butler, Abraha Habtemariam, Mark E. https://orcid. Crofts, The increase in rate occurred as the concentration of ubiquinol in the pool increased on reduction, and could be accounted for in terms of the increased rate of The succinate dehydrogenase. Under anaerobic conditions, reduced quinones (quinols) reduce the cysteines of the PAS domain, resulting in the breakage of disulfide bonds between ArcB homodimers. a reduced quinone, and a neutral quinone . Q(B)H(2) exchanges with PQ from the pool in the membrane. Heliobacteria use MQ exclusively as their quinone (Hiraishi 1989). Using mass spectrometry, we show that the quinone pool also does not Under reducing conditions, the contribution of the reduced quinone-like fluorophores increased concurrentwith a decrease in the oxidized quinone-like fluorophores, indicating that DOM fluorescence Notably, all respiratory chain dehydrogenases such as NADH:ubiquinone oxidoreductase (complex I) and succinate dehydrogenase (complex II) facilitate substrate oxidation and Q pool reduction (Q reducing enzymes) while cytochrome bc1 complex (complex III) in conjunction with cytochrome c and cytochrome c oxidase (complex IV) or an alternative oxidase (AOX) As very low amounts of electrons from the reduced quinone pool are required for NifL reduction and the most electrons will flow to the terminal electron acceptors, we propose that the electron flow onto NifL is unspecific. We demonstrated that complexes between Under anaerobic conditions, the transfer of electrons from NADH to the quinone pool has been shown to be contributed by two enzymes, NQR and NDH2. A. Solar energy In K. 1986 Oct;18(5):403-18. 35 nmol CoQ 10 /mg Whereas the first (from Q B to Q B −) and second (from Q B − to Q B H 2) reduction steps have been largely investigated in bacterial RCs [4], [5], the release of Q B H 2 from its binding pocket towards the membrane and its replacement by an oxidized quinone from the Q pool is less characterized [6]. sulfurreducens uses ImcH to transfer electrons from the quinone pool [48]. Europe PMC. European Journal of Biochemistry 270(7): 1555 In most living organisms, catalytic reactions involved in cell energization generate electrons which are funneled to the quinone pool. Based on the above, it was proposed that the quinone pool is a key target of plant flavonoids inhibiting Gram-positive bacteria, and which likely involves multiple mechanisms including some enzyme i. 2 mg/ml of mitochondria, 4 μM of Q 2, 10 mM of EtOH or 10 mM of G3P (pseudo-state 4) and1 mM of ADP (state 3). 5–1 MDa) redox-driven proton pump receives electrons from the oxidation of foodstuffs, via reduced NADH, and transfers them to quinone (Q), a reaction that is coupled to proton translocation across the membrane The quinone is reduced either to an unstable semiquinone by one hydrogen atom or to a quinol by two electrons and two protons. Hence, it is assumed that the determined DMK8, MK8, represents the total of oxidized plus reduced Quinone redox states were assessed in presence of 0. 40) than the S 2 Q B H 2 back-reaction, which we predict to decay with kinetics between the recombination rates of Q A •− and Q B •− with S 2 [i. Biochim Biophys Acta 811:13-31. B Stoichiometry of homolactic In the light-harvesting 1 reaction center (LH1-RC) complex of purple bacteria, QB is converted to QBH2 upon light-induced reduction and QBH2 is transported to the quinone pool in the membrane Abstract. Author links open overlay panel Pedro Heredia a, Javier De Las Rivas and a so- dium dithionite-reduced quinone (250 µmol/L PBQH 2 ) on the Chl-F curve of PSII-enriched membranes is shown in Figure 3. The results reveal a d The quinone pool delivers another reduced quinone molecule to the Qo site to restart cytochrome bc 1 turnover. Thus, both quinol oxidation and quinone reduction take place, but because only one of the two electrons entering CIII passes on to quinone reduction, the net reaction results in quinol oxidation. In the diazotroph Klebsiella pneumoniae, the nif specific transcriptional activator NifA is inhibited by the flavoprotein NifL in response to molecular oxygen and ammonium. nitroreducens genomes which is homologous to the cytochrome bc 1 and b 6 f complexes of chemotrophs and Oxygen control of nif gene expression in Klebsiella pneumoniae depends on NifL reduction at the cytoplasmic membrane by electrons derived from the reduced quinone pool Grabbe, R. Although the MQ pool is ~ 50–60% reduced in membranes prepared anoxically, its reduction state can be manipulated by simple It is hypothesized that the quinol/quinone ratio is important for providing the signal to NifL and that reduced quinone derivatives, dimethylnaphthoquinol and menadiol, are able to transfer electrons to the FAD-moiety of purified N ifL. Antioxid Redox Signal, 8 (2006), pp. It is also interesting to note that no clear indication of a quinhydrone Q---QH 2 complex is observed. Mitochondrial acylcarnitine-related H(2)O(2) production was substantially higher and the mitochondrial quinone pool was smaller and more reduced. coli , respectiv ely , w ere sho wn to be responsive to Quinone Reduction by the Na +-Translocating NADH Dehydrogenase Promotes Extracellular Superoxide Production in Vibrio cholerae. Sign in | Create an account. We investigated the effect of short-term changes in temperature on alternative (Alt) and cytochrome (Cyt) pathway respiration, both in intact tissues and isolated mitochondria of 14-d-old cotyledons of soybean (Glycine max L. The study authors confirmed that oxidized quinone is required to maintain cancer cells, thereby paving the way for novel potential anticancer strategies aimed at keeping the quinone pool reduced. (B) The PQ and PQH 2 molecules accumulated in the thylakoid membrane are referred to as quinone pool [40]. cholerae membranes. Upon oxidation of superoxide anion at the heme 2, electrons are transferred through the two hemes to reduce the membrane quinone pool with protons being sequestrated from the The redox state of the menaquinone pool is the redox signal for nif-regulation in K. Data are from a single The one-electron reduction of quinones can be catalyzed by a number of enzymes, including microsomal NADPH cytochrome P450 reductase (P450R), microsomal NADH cytochrome b5 reductase (b5R), and Simultaneously, the second electron is passed on from heme b L via heme b H to a second quinone molecule at the quinone reduction site (Q i). On the basis of these data, we postulate that under anaerobic and nitrogen-limited conditions, NifL inhibition of NifA activity is relieved by reduction of the FAD-cofactor by electrons derived from the reduced quinone pool, generated by anaerobic respiration, that favours membrane association of NifL. In situ, the reduced ubiquinone would be expected to equilibrate with the membrane CoQ-pool and to be re-oxidized by the mitochondrial Complex III. A) Proposed reaction mechanism of CybB. 7; Fig. ; Schmitz, R. In the presence of DCMU and methylviologen (MV), which is an efficient PSI electron acceptor and which Quinone Pool, a Key Target of Plant Flavonoids Inhibiting Gram-Positive Bacteria Molecules. Schmitz Institut fu¨r Mikrobiologie und Genetik, Georg-August Universita¨tGo¨ttingen, Germany In Klebsiella pneumoniae, the flavoprotein, NifL regulates NifA mediated transcriptional activation of the N 2-fixation (nif) genes in response to molecular O 2 and Because Complex I couple with the quinone pool, the reduced state of ubiquinol must also be lower. This review highlights the role of quinones and their oxidation state in activating and deactivating ArcB and compares competing models of the regulatory mechanism. Interestingly, genes associated with Complex IV showed higher expression in the FA 80 group, indicating that Complex IV received electrons from sources other than the quinone pool. Advertisement. electron transport. The redox state of the quinone pool becomes reduced when electron acceptors are absent and cannot complete the ETC. The high potential E m (∼90 Download: Download high-res image (279KB) Download: Download full-size image Fig. Nevertheless, in PufX + chromatophores it is clear that the quinone pool reduced under illumination is quite large, at least large enough to prevent any visible sign of Q A − spectral contributions. These quinone radical anions are reduced to quinone dianions and as dianions are more reactive, the reversibility of the last two waves is significantly reduced compared to that of first two waves. Currently it is assumed that the redox level of the quinone pool is responsible for the activation of the sensor kinase ArcB [13, 17, 19]. In protic solvents, quinol Cyanide inhibits electron transfer to these complexes, and as a consequence, the ratio of reduced to oxidized quinones in the Q pool will increase. cholerae increased by approximately 60% upon addition of KCN Oxygen control of nif gene expression in Klebsiella pneumoniae depends on NifL reduction at the cytoplasmic membrane by electrons derived from the reduced quinone pool. Bauer Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA The reduced quinone pool can subsequently be used by membrane-bound oxidoreductases. The two types of ferrihydrite are referred to as hydrophilic ferrihydrite (Fh-LIC) and hydrophobic ferrihydrite (Fh-BIC) in the following text. E. reduction. 4° ± 2. Interplay between quinol-oxidizing and quinone-reducing pathways. In Klebsiella pneumoniae, the flavoprotein, NifL regulates NifA mediated transcriptional activation of the N2-fixation (nif) genes in Regulation of electron transfer by the quinone pool J Bioenerg Biomembr. d. Note that e flow from cytochrome h/ci back to the reaction center occurs Signaling by the arc two-component system provides a link between the redox state of the quinone pool and gene expression. This is contrary to expectation. coli consists of three quinone types, the benzoquinone ubiquinone (UQ) and the naphtoquinones and at 248 nm for naphtoquinones (DMK and MK). Abbreviations: H + , Q/QH 2 —quinone/quinole. Given the presence of multiple homologous proteins of the dual-component system in the genome, it can be speculated that Geobacter likely possesses a receptor “potential sensing pathway” dependent on the Arc Quinones participate in diverse electron transfer and proton-coupled electron transfer processes in chemistry and biology. Therefore, the presence of FA created an alternative electron pool that The presence of the DsrOP dimeric module suggests a MK/MKH 2 oxidoreductase function, which may involve electron transfer from a periplasmic substrate to the quinone pool, in which case quinone cycling could occur between the DsrJOP and DsrMK modules. In Heliobacterium modesticaldum, the major quinone is MQ-9 with a smaller amount of MQ-8 (Sarrou et al. local quinone pool that does not exchange with the quinone pool outside [[24], [57], 58]. All reduced quinone species were also detected with an Agilent 1200 series fluorescence detector, coupled in series with a UV/Vis detector, using 238 and 375 nm as the excitation- Moreover, the rates of quinol oxidation and quinone reduction are equivalent, indicating that the quinone pool is more reduced when compared to the redox state during growth on acetate and butyrate. Authors Li Zhang 1 2 , Yu Yan 1 , Jianping Zhu 2 , Xuexue Xia 1 , Ganjun Yuan 1 2 , Shimin Li 2 , Beibei Deng 2 , The quinone pool of E. the quinone (Q) pool and cytochrome c. Cells sampled from these cultures were then assessed for the The electron transport chain in the mitochondrion is the site of oxidative phosphorylation in eukaryotes. Results shown are means ± SD of three separate experiments done on the same As very low amounts of electrons from the reduced quinone pool are required for NifL reduction and the most electrons will flow to the terminal electron acceptors, we propose that the electron flow onto NifL is unspecific. cv Stevens). viridis reaction center is coupled to the cytochrome h/Cl complex through the quinone pool (Q). Qb is located near the nonheme Fe2+ and the ligand to the Fe2+, Dl-His215, donates an H-bond to the QB carbonyl O atom that is quinone reduction Yanfei Zhang, Ali Qadri, and Joel H. 1. Fatty acid species with significant opposite directions of change in oxidized versus reduced PQ pool are in bold. All reduced quinone species were also detected with an Agilent 1200 series fluorescence detector, coupled in series with a UV/Vis detector, using 238 and 375 nm as the excitation- (1) The role of the ubiquinone pool in the reactions of the cyclic electron-transfer chain has been investigated by observing the effects of reduction of the ubiquinone pool on the kinetics and extent of the cytochrome and electrochromic carotenoid absorbance changes following flash illumination. Exogenous quinones have been used extensively as tools to investigate physiological Microorganisms with electron transfer capabilities, such as metal-reducing microorganisms, use specialized systems to exchange electrons between minerals and cells. 10 V), G. The original hypothesis of the common quinone pool, introduced by Kroeger and Klingenberg in 1971, was replaced by assuming the presence of two different quinone pools: one acting for the oxidation of NADH and the second for the oxidation of succinate and for the oxidation of substrates of other dehydrogenases that use ubiquinone as an electron Pool quinones FIGURE 22. thaliana grown under low light, Kruk and Karpinski 44 reported a complete reduction of a photochemically active PQ pool, while Szechyńska-Hebda et al. The quinone pool operates in the first steps of this electron transfer through the electron transport chain by transporting electrons Van den Bergen CW, Wagner AM, Krab K, Moore AL (1994) The relationship between electron flux and the redox poise of the quinone pool in plant mitochondria. org. e. Based on the atomic coordinates of the Photosystem II crystal structure, we analyzed the proton transfer (PT) energetics adopting a quantum mechanical/molecular mechanical approach. Experimental A highly reduced quinone pool and large proton motive force can push electrons back-ward through R-CI, leading to reverse electron transfer. However, at the current experimental stage we cannot rule out completely the possibility of an additional oxidoreductase We also detected the reduced quinone produced in the vicinity of the mitochondrial membrane fragment, as a response to the addition of NADH and succinate, using Scanning Electrochemical Microscopy (SCEM). The present review discusses hiological and toxicological aspects of quinone metabolism. 2010). In this way, the current understanding on the pathophysiology of MIRS and a brief review about the use of such drugs in MIRS-reduction allow us to think that a low dose of corticosteroids Two major views of the way in which quinones function have emerged, and it is suggested that interchain electronic mobility occurs, but is provided by collisions between the multiprotein complexes themselves, but with the electron transfers occurring through bound quinone species. 3390/molecules28134972. RegB kinase activity is controlled in part by monitoring the ratio of oxidized to reduced ubiquinones in the ubiquinone pool. doi: 10. These back-reactions, however, would only occur when the plastoquinone pool is reduced, because quinol/quinone exchange occurs orders of magnitude faster (∼10 ms; ref. Quinone reduction to semiquinone (e1, wave 1), and then to quinol (e2, wave 2). Kramerd, and Wolfgang Nitschkea aLaboratoire de Bioe´nerge´tique et Inge´nierie des Prote´ines, Unite´ Propre de Recherche 9036, Institut Fe´de´ratif de Recherche 88, Centre National de la The quinone pool is one of such disregarded features. The exact mechanism and the net proton translocation associated with reverse electron transfer by bc 1 is not well understood, but is thought to be at the expense of the PMF (Ferguson and Ingledew, 2008). , between ∼1 s and ∼30 s ]. The amounts of DMK and MK in MG1655 were about 9 fold higher under anaerobic than under aerobic conditions. Physical and chemical data are considered in order to attempt to explain the physiological 1) The role of the ubiquinone pool in the reactions of the cyclic electron-transfer chain has been investigated by observing the effects of reduction of the ubiquinone pool on the kinetics and extent of the cytochrome and electrochromic carotenoid The quinone pool of E. Animals and plants use ubiquinones (1,4-benzoquinones or p-benzoquinone) in their mitochondrial membrane quinone-pool, while bacteria use a mixture The mixture of quinones was analysed by UV/Vis absorption spectroscopy at 270 nm (see Methods). Cytochrome c, instead, has a dual role in cell . cholerae increased by approximately 60% upon addition of KCN The basic structure of PQ is a benzoquinone ring attached to a polyisoprenoid side chain. PMID: 3021716 DOI: 10. Cottingham IR (1985) The kinetics of quinone pools in electron transport. e The Qo site turns over again, delivering a second set of electrons to the high potential c-chain and the low potential b-chain, ArcA phosphorylation is reduced in strains synthesizing only MK or MK plus DMK. We have tested this hypothesis by illuminating heliobacterial membranes and examining the redox state of the quinone pool directly. as NADH dehydrogenase-dependent quinone reduction leads to a higher production of proton motif force per electron Photosystem II uses light to drive water oxidation and plastoquinone (PQ) reduction. The Arc system is commonly induced under conditions provoking a reduced state of the quinone pool of the electron transport chain. To understand the relationship between these redox processes, an experimental study was In any case, the reduction of the quinone (Q + 2e + 2H += QH 2) form by the photosynthetic chain is obviously crucial. [8] In the first step, a short-lived semiquinone intermediate is formed. Ketogenesis and fatty acid-dependent respiration were lower, indicating a lower Here, the authors report on the changes in both the size and the redox state of the quinone pool when the environment changes from being well aerated to one with low oxygen availability. These reduced forms, however, always showed nearly complete oxidation during quinone isolation, and are therefore not included in this report. 0° and 120. Complex I, Complex II and Complex III), in beef heart mitochondria (BHM) we come up to about 0. 800 of the ISP EPR spectrum was lost on reduction or changed on extraction of the quinone pool. 17 The R. Sadler* Quinones (Q) are a class of fully conjugated cyclic dione compounds that are widely distributed in nature. The J–I–P transient is called the thermal phase and, in addition to Q A reduction, probably reflects reduction of secondary quinone electron acceptor in PSII (Q B ) and PQ pool (Neubauer and We have studied quinone pool reduction in chromatophores from PufX + and PufX-strains of Rhodobacter capsulatus by time-resolved FTIR difference spectroscopy under and after continuous illumination. However, in Reduced flavin would then become re-oxidized by passing electrons, perhaps one at a time, to the putative iron–sulphur cluster that, in turn, would be exposed to the quinone. We also established the extent to which temperature alters the interaction between the oxidizing pathways and the . 2c,d Quinone reduction state when totally reduced quinones were obtained following either inhibition of mitochondrial respiration by antimycin A or hypoxia with G3P as respiratory substrate (A) or ethanol (B). This study aimed to determine how respiratory The translationally-coupled synthesis of the two regulatory proteins imply that the inhibition of NifA activity by NifL occurs via direct protein-protein interaction in vivo, which implies that nitrogen-fixing microorganisms tightly control both the synthesis and activity of nitrogenase to avoid the unnecessary consumption of energy. . Q(A) is a one-electron carrier, whereas Q(B) undergoes sequential reduction and protonation to form Q(B)H(2). 7° ± 4. PQ reduction involves two PQ cofactors, Q(A) and Q(B), working in series. The extent to which CoQ is bound to mitochondrial proteins is an important parameter in its function. Thus, a more reduced quinone The electrons that have been extracted from water are shuttled through a quinone pool and the cytochrome-b 6 f complex to plastocyanin, a small, soluble, copper-containing protein 16. Within mammals, only CoQ 9 and CoQ 10 are found, with CoQ 9 only distributed among rodents. The direction of change reported after 24 h for each treatment are derived from values reported in Fig. The enzymatic reduction of molecular nitrogen Scientific Reports - Modeling the Interplay between Photosynthesis, CO2 Fixation, and the Quinone Pool in a Purple Non-Sulfur Bacterium Skip to main content Thank you for visiting nature. In addition, upon exposure to variety of stress (reduced O 2 , NO, and CO), the DosSR TCS gets activated leading to an increase in the cellular NADH pools, thus playing an important role during The low rate of oxidation/ reduction of both redox components, previously consid- ered to indicate that they are located only on a side path, was proposed to be due to the large size of the quinone pool and the rapid equilibrium between ubiquinone and cytochrome b [1,2]. 10 V vs SHE), G. Depending upon prevalent redox conditions, para-quinones can be fully reduced (hydroquinone; QH 2), fully oxidized (p-quinone; Q), or in an intermediate (p-semiquinone radical; QH) oxidation state. Google Scholar [52] These back-reactions, however, would only occur when the plastoquinone pool is reduced, because quinol/quinone exchange occurs orders of magnitude faster (∼10 ms; ref. Structures of the three forms of semiquinone, QH 2 +,·QH, and ·Q:−. We find that the activity contributed by each under nanaerobic conditions is 77 and 23%, respectively, similar to the activity levels under anaerobic conditions. 1002/anie. Hence, AOX represents a natural rescue mechanism from respiratory stress. Finally, the model predicts that during growth on the When the receptor redox potential is high (> −0. We could not find membrane-bound quinol oxidases. In this Review, Shiet al The quinone pool of E. In aprotic media, quinones undergo two-step reduction without protons. Schmitz Institut fu¨r Mikrobiologie und Genetik, Georg-August Universita¨tGo¨ttingen, Germany In Klebsiella pneumoniae, the flavoprotein, NifL regulates NifA mediated transcriptional activation of the N 2-fixation Quinone Pool, a Key Target of Plant Flavonoids Inhibiting Gram-Positive Bacteria Molecules. (2 depends on NifL reduction at the cytoplasmic membrane by electrons derived from the reduced quinone pool Roman Grabbe and Ruth A. 40) than the S 2 Q B H 2 back-reaction, which we predict to decay In a simulated gut environment containing a mixed pool of quinone derivatives, this tailored EET pathway can selectively sense pharmacologically relevant quinone analogs, such as DHNA and menadione, amongst other structurally similar quinone derivatives. For neutrophilic iron Peaks for reduced DMK8 and MK8 were found to elute around 6 and 7 min, respectively (data not shown). Oxidized to Reduced Ubiquinones in the Ubiquinone Pool Jiang Wu and Carl E. 05, “**” represents p ≤ 0. Biological aspects of quinones The widespread occurrence of p-benzoquinones in biological Notably, under aerobic conditions, about 40% of the quinone pool was in the reduced state, while no reduced UQ was detected under anaerobic conditions. 4 mM at 14. Water oxidation and quinone reduction result in the net transport of 4 H + per O 2 from the cytoplasm to the lumen. PQH 2 becomes reoxidized at the cyt b 6 f complex [4] The fully reduced quinol is then exchanged with an oxidized quinone from the membrane pool and passes its electrons to the next redox component in the cyclic electron transfer pathway, during of the quinone within the HbRC? The fact that MQ is bound loosely by the HbRC raises the possibility that it serves as an alternate electron acceptor, similar to the mobile quinones of Type II RCs. The difference between both types of risk factors evidently lies If the rates of N2 cluster oxidation are low due to a predominantly reduced quinone pool, RET occurs when there is an overabundance of ubiquinol in the Q/QH 2 pool due to reduction by electrons from Complex II. It is shown that such transitions are accompanied by a rapid increase in the demethylmenaquinone pool, and a slow increase in the MK pool. 5 μg/mg protein of Antimycin A or hypoxia were used to totally reduce the quinone pool. The steady-state reduction of exogenous ubiquinone-2 by duroquinol as catalysed by the ubiquinol: cytochrome c oxidoreductase was studied in bovine heart mitoplasts. 3) are a special type of quinone that when reduced by two electrons to the corresponding hydroquinone generates stable lipophilic antioxidants that aid in the protection of lipid membranes against peroxidative damage. Two kinds of ferrihydrite with contact angles of 22. Menaquinone 7 (MQ-7) is dominant under anoxic conditions. To our knowledge, it is the first time that quinone pool reduction has been directly followed in real time in Rba. If we consider bound CoQ in a 1:1 stoichiometry with the mammalian mitochondrial respiratory complexes interacting with the quinone (i. proton motive force. However, at the current experimental stage we cannot rule out completely the possibility of an additional oxidoreductase system mediating electrons Lipophilic antioxidant quinones such as α-tocopherol quinone and ubiquinone (Figure 7. plastoquinone pool is reduced because quino l/ quinone exchange occurs orders of magn it ude faster ( ≈ 10 ms, (42)) than the S 2 Q B H 2 back-reaction, which is predicted to decay with kinetics Cyanide inhibits electron transfer to these complexes, and as a consequence, the ratio of reduced to oxidized quinones in the Q pool will increase. 1. pneumoniae, the reduced quinone pool generated by the respiratory chain has been proposed to reduce the FAD domain of NifL under anaerobic conditions, leading to the release of NifA and Menaquinone as pool quinone in a purple bacterium Barbara Schoepp-Cotheneta,1, Cle´ment Lieutauda, Frauke Baymanna, Andre ´Vermegliob, Thorsten Friedrichc, David M. Authors Li Zhang 1 2 , Yu Yan 1 , Jianping Zhu 2 , Xuexue Xia 1 , Ganjun Yuan 1 2 , Shimin Li 2 , Beibei Deng 2 , The EET chain of Geobacter can link the oxidation of the intima quinone pool with the reduction of extracellular receptors [1, 57]. Cytochrome bc 1 is one of the key enzymes of mitochondrial respiratory chain, where it plays a major role as proton translocating machinery utilizing the energy stored in the difference in We derive a kinetic model for electron transfer through the ubiquinone pool based on detailed consideration of reactions at the quinone reductase and quinol oxidase sites and It can be seen that the growth rate of all three single quinone strains is reduced compared to that of the wild type strain. We further hypothesize that the quinol Light-dependent MQ reduction in heliobacterial membranes. Kramerd, and Wolfgang Nitschkea aLaboratoire de Bioe´nerge´tique et Inge´nierie des Prote´ines, Unite´ Propre de Recherche 9036, Institut Fe´de´ratif de Recherche 88, Centre National de la In particular, the loss of normal quinone function invariably has toxicological consequences, in which the activation of oxyqen hy quinone redox reactions plays a central role. It mediates the reaction between NADH or succinate generated in the citric acid cycle and oxygen to power ATP A great deal of work on mitochondrial systems has established that the quinone pool can be oxidized and reduced at rates compatible with a direct role in electron transfer, and it has been shown that ubiquinone can be reduced by the substrate dehydrogenases, and ubiquinol oxidized by the ubiquinol:cytochrome c oxidoreductase [10-16]. 1007/BF00743012. 1007/BF00743012 Abstract Strong evidence for a random collisional mechanism for ubiquinone-mediated electron transfer is provided by the characteristic kinetic properties of The alternative oxidase (AOX) is a respiratory enzyme, absent in mammals, that accepts electrons from a reduced quinone pool to reduce oxygen to water, thereby restoring electron flux when impaired and, in the process, blunting ROS production. This leads to a reduced electron flow through the ETC, and subsequently lower ATP generation. Different types of natural quinones, comprising mainly benzoquinones, naphthoquinones, anthraquinones and polycyclic quinones, are widely distributed in different organisms. 406 Ragan and Reed Following a second reduction event at the Q i site, two protons are taken up from the stroma at this site and the reduced quinone is released into the lipid bilayer to join the reduced quinone pool. Cellular consequences of these mitochondrial alterations were investigated in perifused, freshly isolated hepatocytes. , the rate of oxygen uptake was directly proportional to the amount of the total quinone pool in the reduced state. Due to its extreme hydrophobicity, natural CoQ can be present in three physical states only: forming Results demonstrate that in the purple γ-proteobacterium Halorhodospira halophila, menaquinone-8 (MK-8) is the dominant quinone component and that it operates in the QB-site of the photosynthetic reaction center (RC), and suggests a specific scenario for the evolutionary transition of bioenergetic chains from the low-potential menaquinones to higher Complex I (NADH:ubiquinone oxidoreductase) functions as an important member of the aerobic respiratory chains of many organisms. Fluorescence spectroscopy reveals ubiquitous presence of oxidized and reduced quinones the quinone pool is not restricted to the ArcB sensor, as the un- orthodox histidine kinases BvgS and EvgS of Bor detella per- tussis and E. &, UQ 8 H 2 ; $, oxygen saturation; X OD 600. , the photosynthetic RC and the cyt bc 1 complex. The signal intensity of the organic radical detected in NADH-reduced membranes from wild-type V. In case that the quinone pool is predominantly reduced, it is not capable of oxidizing reduced N2. All reduced quinone species were also detected with an Agilent 1200 series fluorescence detector, coupled in 2. 4° were prepared (Figures 1 A, 1B, and S1). Either 0. [7,19] In this scenario, it is debated whether the Q-binding site can act as a further source Fluorescence induction of Photosystem II membranes shows the steps till reduction and protonation of the quinone pool. When this occurs, electrons can be transferred from ubiquinol to N2. sulfurreducens utilizes CbcL to capture electrons in In these metabolisms, the cytochrome bc 1 complex is proposed to be involved in reverse electron transfer to reduce the quinone pool (Bird et al. Behind an apparently simple electrochemical reaction, the electrochemical behavior of quinones is indeed very complex in aqueous media. A partial reduction of quinones produces semi-quinone radicals (UQ −), which are highly redox active molecules that can react with oxygen and form reactive oxygen species (ROS). R. The autophosphorylation of the SK ArcB is followed by a phosphoryl group transfer onto its cognate RR ArcA resulting in a specific response. pneumoniae by directly transferring electrons onto NifL under anaerobic conditions. , between ∼1 s and The quinone pool of E. Download: Download full-size image Likewise, ortho-quinones can be The fact that an individual quinone species is dominant, however, does not necessarily imply that it functionally represents the pool quinone. and succinate dehydrogenase (complex II) facilitate substrate oxidation and Q pool reduction (Q reducing enzymes) while If the rates of N2 cluster oxidation are low due to a predominantly reduced quinone pool, RET occurs when there is an overabundance of ubiquinol in the Q/QH 2 pool due to reduction by electrons from Complex II. SDH’s four subunits (A–D) are conserved from microorganism to human. Kroger and Klingenberg (5,6) have previously shown the oxidation of reduced ubiquinone by cytochrome bc, complex, in bovine heart mitochondria, to be a first-order process with respect to the substrate; i. from publication: Changes in the redox state and composition of the quinone pool of Escherichia coli The reduction state of the UQ 8 pool was measured in minimal medium supplied with 50 mM glucose in shake cultures. On the other hand, we can determine the flow rate of plastoquinone reduction because it is the limiting step for P 700 + reduction. 2012). The reduction of ubiquinone-2 by duroquinol proceeds both in the absence of inhibitors of the enzyme, in the presence of outside inhib The benzoquinone ring can be reduced by two reversible reduction steps leading to the formation of ubiquinol (UQH2), the reduced form of ubiquinone. Author links open overlay panel A. 201300747 Reduction of Quinones by NADH Catalyzed by Organoiridium Complexes** Zhe Liu, Robert J. Rich 1984 Biochim Biophys Acta: 1984: Rich PR (1984) Electron and proton transfers through quinones and An important study by Ding and Dutton [[115], [116], [117]] had shown that the g x line at 1. When oxygen is not being utilized as an electron acceptor, ArcB In A. mBio, 1 (5) (2010) e00272-10. Quinones have an Cytochrome c nitrite reductase, NrfA, is a soluble, periplasmic pentaheme cytochrome responsible for the reduction of nitrite to ammonium in the Dissimilatory Nitrate Reduction to Ammonium (DNRA) pathway, a vital reaction in the global nitrogen cycle. In the second step, the semiquinone is reduced into a quinone dianion. 2023 Jun 24;28(13):4972. 7 mM Na +, indicating that the concentration of the coupling cation influences the redox state of the quinone pool in V. Quinones, the In this case, the MK pool becomes reduced through a membrane-bound H 2-ase, a formate dehydrogenase or an alternative dehydrogenase, and menaquinol (MKH 2) oxidation is accomplished by a RDase The role of the quinone pool in the cyclic electron-transfer chain of Rhodopseudomonas sphaeroides A modified Q-cycle mechanism. Menu bound quinone pool. The hydrophobicity of ferrihydrite affects the rate of Fe(III) reduction by Shewanella oneidensis MR-1. CoQ exists in three redox states, fully oxidized, semiquinone, and fully reduced: nevertheless, the existence of different possible levels of Cytoplasmic substrates are oxidized and the resulting electrons are transferred via membrane bound oxidoreductases to a pool of quinones in the cytoplasmic membrane. c. [1] They can function as electron carriers in The bioenergetics of anaerobic metabolism frequently relies on redox loops performed by membrane complexes with substrate- and quinone-binding sites on opposite sides of the membrane. The phosphorelay reaction for the phosphoryl group transfer from ArcB to CoQ exists in three redox states, fully oxidized (ubiquinone), semiquinone radical (ubisemiquinone), and fully reduced (ubiquinol): nevertheless, the existence of different possible levels of protonation increases the possible redox forms of the quinone ring [15]. Calculated and Tested Minimum Inhibitory Concentrations (MICs) As shown on Figure 1, twelve plant flavonoids, with seven structural subtypes including dihydroflavones, flavonols, flavones, isoflavones, chalcones, flavanes and xanthones, were selected for verifying the inference that the quinone pool is a key target of plant flavonoids inhibiting Gram-positive As very low amounts of electrons from the reduced quinone pool are required for NifL reduction and the most electrons will flow to the terminal electron acceptors, we propose that the electron flow onto NifL is unspecific. Laviron extensively investigated the behavior of benzoquinone and developed the theory Modifiable risk factors include hypercholesterolemia, specifically related to elevation of low-density lipoprotein cholesterols (LDL-C), hypertension, tobacco abuse, diabetes mellitus, obesity, lack of physical activity, metabolic syndrome, and/or mental distress and depression . Under aerobic conditions, AV34 showed a similar UQ This flow rate was determined when the quinone pool was fully reduced in the light ([PQH 2] = 1) which gives k ox ~ 2 s −1. Another possibility is that direct electron transfer occurs between the two modules without involvement Quinone Reduction DOI: 10. The main form of PQ in plants is PQ-9 which contains a nonaprenyl side the available data indicate that PQ-9 pool reduction/oxidation levels play an important regulatory role in balancing excitation energy between the photosystems by both short-term Quinone reductase 2 (NQO2) is an enzyme that might have intracellular signaling functions. Deeth, Jennifer S. In contrast, QB reduction involves two consecutive one-electron reduction reactions with a series of associated proton uptake reactions (reviewed in 1-6). Instead, we identified an unusual Rieske/cytochrome b (Rieske/cytb) complex encoded in the M. capsulatus membranes. b. Thereafter, the reduced quinones (quinols) serve as substrates for reduction of the terminal acceptors. On the other hand, corticosteroids have been successfully used to reduce IRI in kidneys , liver , and brain , with the added benefit of attenuating pathogenic fibrosis during the reparative phase . This transfer allows quinone reduction to quinol; transfer through the respiratory chain is indicated by blue arrows. This gigantic (0. Authors C I Ragan, J S Reed. energy flow. All reduced quinone species were also detected with an Agilent 1200 series fluorescence detector, coupled in series with a UV/Vis detector, by electrons derived from the reduced quinone pool Roman Grabbe and Ruth A. “*” represents p ≤ 0. Even less characterized is the reduction of the Q pool in These back-reactions, however, would only occur when the plastoquinone pool is reduced, because quinol/quinone exchange occurs orders of magnitude faster (∼10 ms; ref. 45 documented the PQ PA reduction at 40%. Newton, and Peter J. To assess whether MK or UQ constitutes the quinone pool in photosynthesis, we characterized the enzymes directly interacting with the pool, i. However, at the current experimental stage we cannot rule out completely the possibility of an additional oxidoreductase system mediating electrons The bacterial quinone pool is the primary modulator of ArcAB activity, but questions remain for how this regulation occurs. Research Article. The reduced state of N2 leads to a reduction of N1a by FMNH* 21 . homeostasis: in mitochondria, it shuttles electrons from complex III 2 to . A wide range of planar aromatic compounds bind NQO2, and we have Menaquinone as pool quinone in a purple bacterium Barbara Schoepp-Cotheneta,1, Cle´ment Lieutauda, Frauke Baymanna, Andre ´Vermegliob, Thorsten Friedrichc, David M. The natural CoQ is 2,3-dimethoxy-5-methyl-6-polyprenyl-1,4-benzoquinone, where the polyprenylated side chain is 6–10 units long. Conversely, when the receptor potential is low (< −0. Our results are compatible with this still Q B H 2 exchanges with PQ from the pool in the membrane. NADH:ubiquinone oxidoreductase (cI) and succinate dehydrogenase (cII) facilitate substrate oxidation and Q pool reduction (quinone-reducing complexes) whilst cytochrome bc 1 complex (cIII), cytochrome c and cytochrome c oxidase (cIV or COX) are the quinol-oxidizing components of the ETC. Na + to 0. The process by which electrons from the quinone pool are forced against the thermodynamic gradient to reduce NAD+ to NADH is called reverse A. 781-795. CybB structure and the corresponding substrates. com. 01, and “***” represents p ≤ 0. In presence of a strong acid like HClO 4 the calix-[4]-quinone undergoes eight-proton eight-electron reduction. Animal SDH, as its plant counterpart, reduces a specific pool of ubiquinone that competes with other kinetically distinct quinone pools reduced by various mitochondrial dehydrogenases for the reduction of CIII-associated quinones. Quinones function as membrane bound electron carriers between dehydrogenases and oxidases in the aerobic and anaerobic quinone pool reduced. The quinone pool is therefore oxidized rapidly in dark conditions. Less clear are the conditions which lead to loss of the normal metabolic functions of quinones, often resulting in the generation of active oxygen species. QM/MM calculations for the carbonate-ligated Fe 2+, one The quinone pool is therefore the lipid phase counterpart of the pyridine nucleotide pools in the aqueous phases of cells, and the various bound forms of quinone, detected by their stabilized semiquinone states, are the quinone present is reduced or oxidized respectively, without specifying . From the viewpoint of synthetic chemists, the quinone pool has not been an attractive target, mainly because it consists of a collection of unspecified number of molecules (quinones and quinols embedded in membranes) rather than a well-defined set of characteristic molecules as the reaction center. coli consists of three quinone types, the benzoquinone ubiquinone (UQ) and the naphtoquinones using a UV/Vis absorption detector at 290 nm for ubiquinone (UQ) and at 248 nm for naphtoquinones (DMK and MK). Indeed, when purified quinol bo 3 oxidase was added in order to regenerate the quinone pool, superoxide production was completely suppressed over the entire experiment (experiment no. Figure 2. rhgrxagweewixkasausgooislhcxshdkplyznvpwahjqzhsdijctzvrkg