Reduced quinone pool. rubrum [44] the chemical species is Q-10, while in C.

Reduced quinone pool 5 B). These results are at variance with the behavior expected of the kinetic model developed by Biochim. b The Qo site becomes oxidized, transferring two protons across the membrane 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 Roman Grabbe and Ruth A. The formation of ATP depends directly on the oxidation of cytochrome c. Etfs convey those electrons to another flavoprotein, Etf-quinone oxidoreductase (Etf-QO), which in turn passes them into the respiratory electron transport chain via the reduced quinone pool. Complex I is a key proton-pumping enzyme in bacterial and mitochondrial respiratory electron transport chains. This head group consists of a benzoquinone ring, which can accept and donate electrons, a property central to its function in electron transport chains. Experiments with quinone biosynthesis mutants show that menaquinol is the sole electron donor to thiosulfate Jan 19, 2024 · Introduction Quinones are electroactive molecules (related to the hydroquinone/quinone redox couple) which have been widely used for decades for a large range of applications including (bio)sensing approaches under a form either adsorbed on the electrode surface 1 - 5 or in solution. Quinones are not aromatic compounds but are conjugated cyclic diketones. AOX expression did not alter complex I abundance, supercomplexes assembly, or basal respiration rates, but effectively diverted electrons from the quinone pool, decreasing RET flux via complex I and limiting ROS Preferential quinone binding will allow PSII to function when the pool is significantly reduced. A variety of quinonelike structures have been prepared, the most common of which are the 1,2 - and 1,4-quinones as exemplified by 1,2 The choice of candidate quinone pool was based on previous reports,26 where molecular motifs more likely to give high reduction potentials and high solubility have been identified. . 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. Dec 23, 2021 · Excess reduced quinone would induce reverse electron transfer by stimulating ROS production from Complex I, which in turn would cause a partial degradation of mitochondrial Complex I itself. a One reduced quinone molecule is delivered to the Qo site from the Q-pool. coli is under anaerobic or anoxic conditions, reduced quinone accumulates, which induces the phosphorylation ArcB and then triggers phosphorely to further phosphorylate ArcA. Without quinones, no nitroaromatic tested was reduced except for the IMC 3-nitro-1,2,4-triazol-5-one (NTO). (A) A true Fe (II):menaquinone oxidoreductase accepts electrons from iron and reduces the quinone pool Jan 19, 2024 · Introduction Quinones are electroactive molecules (related to the hydro-quinone/quinone redox couple) which have been widely used for decades for a large range of applications including (bio)sensing approaches under a form either adsorbed on the electrode surface[1–5]or in solution. However, a large fraction of the PQ pool is located outside the thylakoid membranes, in the plastoglobules and the chloroplast envelopes, reflecting a wider range of Four electrons from this oxidation are transferred to the quinone pool. Mar 1, 2025 · Under illumination, photoelectrons generated by CdS nanoparticles first enter the inner membrane quinone pool through c-type cytochrome complexes on the outer and inner membranes to drive NADP reduction, then reduce ferredoxin (2Fe-2S) under the action of the Rnf complex, and finally enter the anammoxosome through the quinone pool and For every two electrons delivered to Complex III in the form of reduced quinone QH2and guided eventually to two oxidized water soluble cyto-chromes c, the Qo site is host to two full quinone oxidations and the Qi site to one full quinone reduction. If the quinone pool were artifically depleted, the expected consequences would be a buildup of _______ and _________ H2O production A- NADH; increased B- NADH; decreased C-NAD; increased D- NAD; decreased NADH; DECREASED Dec 7, 2001 · The function of the coenzyme Q (CoQ) pool in the inner mitochondrial membrane is reviewed in view of recent findings suggesting a supramolecular organization of the mitochondrial respiratory complexes. These carriers form two redox pools, each confined to the environment of different polarity. This would cause a decrease in the proton gradient, which would lead to a decrease in the flow of electrons. Complex III itself consists of three important groups: (1) cytochrome c1 that contains a single heme group (2) cytochrome b Mar 1, 2023 · This mechanism accounts for the dependence of the redox cycling rate on quinone and ascorbate concentrations as well as on the reduction potential of the quinone. However, a large fraction of the PQ pool is located outside the thylakoid membranes, in the plastoglobules and the chloroplast envelopes, reflecting a wider range of Dec 21, 2018 · In both cases, the key protein for energy conservation is a di-heme cytochrome b that performs transmembrane electron transfer and reduces/oxidizes the quinone pool, with the crucial difference Apr 29, 2025 · The quinone head group is the reactive part of ubiquinone, capable of undergoing redox reactions. Aug 1, 2025 · Here we present a cursory review of quinone utilizing flavoprotein oxidoreductases and their quinone binding sites and discuss plausible rationalizations for this binding mode. Oct 5, 1988 · The effect of the size of the quinone pool on the electrogenic reactions in the ubiquinol-cytochrome c2 oxidoreductase of Rhodobacter capsulatus. The quinone pool is an important component in the ETC, which supports the notion that quinones rapidly reflect the redox conditions within the cell. In general, the biological properties of quinone precursors (good, bad, or equivocal) are often mediated by their oxidative metabolism to quinones. A high-fat diet results in both a decrease in mitochondrial quinone pool and a profound modification in mitochondrial lipid composition. Within the PSII complex, electrons are extracted from water at the lumenal side of the thylakoid membrane and transferred to the primary accepting quinone (Q A) at the stromal side. May 1, 2003 · Request PDF | 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 | In Apr 20, 2024 · This detection method is very sensitive to the local availability of the quinone inside the membrane in the vicinity of the electrode. Biochem. Two of the succinate dehydrogenase genes, sdhB and sdhA, are down-regulated, which normally contributes to the reduced quinone pool in the membrane. Preferential quinone binding will allow PSII to function when the pool is significantly reduced. The reduced form quinol in (1d) and the oxidised form quinone in (1e) couple oxidase and dehydrogenase reactions. Feb 12, 2025 · We characterize a cluster of charged residues at the periplasmic side of the membrane that functions as a O 2·– collecting antenna, initiating electron transfer via two b hemes to the active site for quinone reduction at the cytoplasmic side. 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. The reducing or electron potential in (1f) represents available electrons pairs. Sep 5, 2020 · The redox state of the chloroplast plastoquinone (PQ) pool regulates state transitions and gene expression in response to illumination conditions. The #1 social media platform for MCAT advice. An oxidized quinone derived from the quinone pool replaces the transient reduced quinone (step 1). Second, reduced respiratory activity is likely to affect some signaling pathways that rely on the activity of the electron transport chain. The original hypothesis of the common quinone pool, introduced by Kroeger and Klingenberg [39] 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 Mar 17, 2003 · In order to obtain additional evidence that NifL receives electrons from the reduced quinone pool at the cytoplasmic membrane depending on the quinol/quinone ratio, we studied nif induction with glycerol and in the presence of external terminal electron acceptors. fully reduced quinone is accumulated in the quinone pool. If the capacity of transfer to the respiratory chain is exceeded and the PQ pool is completely reduced, charge recombination between Q A− (the reduced form of the first quinone-type electron acceptor in PSII) and the donor side of PSII complexes can occur in 0. May 23, 1983 · At redox potentials higher than 180 mV, where the pool is completely oxidized, the maximal extent of the slow phase is half that at 140 mV, where the pool contains approx. B. In spite of the structural evidence for preferential aggregations of the inner membrane components, most kinetic evidence is in favor of a dispersed organization based on random collisions of An oxidized quinone derived from the quinone pool replaces the transient reduced quinone (step 1). Jul 1, 2022 · The ubiquinone (Q) pool represents a node in the mitochondrial electron transport chain (ETC) onto which the electrons of all respiratory dehydrogenases converge. The quinone pool is therefore oxidized rapidly in dark conditions. As expected, two electrons per quinone molecule were transferred in the electrochemical process whatever the pH. In Klebsiella pneumoniae, the flavoprotein, NifL regulates NifA mediated transcriptional activation of the N2-fixation (nif) genes in response to molecular O2 Jan 1, 2015 · These carriers form two redox pools, each confined to the environment of different polarity. Oct 7, 2013 · During growth, catabolic activity in the cytoplasm liberates electrons in the form of reduced electron carriers such as NADH and FADH 2, which transfer the electrons to the quinone pool (s) in the respiratory chain via specific dehydrogenases. The second method is an electrochemical technique using a redox mediator to indirectly monitor the quinone redox state. succinogenes. rubrum [44] the chemical species is Q-10, while in C. Two electrons from the reduced quinone pool return to AMO (marked by red) and are required to initiate ammonia oxidation. In turn, quinones can interact with ArcB, resulting in a response to changes in metabolic activity. The primary, metastable electron acceptor of the purple photosynthetic bacteria (Rhodospirillaceae and Chromatiaceae) now appears well established as a quinone (Q,). Additionally, the RpoS-controlled katE gene encoding the catalase hydroperoxidase II, which synthesizes the heme d cofactor for both cytochrome bd -type oxidases, is also up-regulated. Apr 27, 2007 · To address the question of whether electrons are directly transferred from the reduced quinone pool onto the flavoprotein NifL or via a NifLspecific protein (reductase or receptor), we studied NifL reduction using a partial reconstituted anaerobic respiratory chain from W. Nov 1, 2021 · If the rates of N2 cluster oxidation are low due to a predominantly reduced quinone pool, this causes reduction of N1a by FMNH· and a conformational switch within the NADH binding pocket that favours NAD+. Abstract The ubiquinone (Q) pool represents a node in the mitochondrial electron transport chain (ETC) onto which the electrons of all respiratory dehydrogenases converge. In subfamily C enzymes, the Q-site is classified as Q p (Fig. This microbe possesses subunits for cytochrome c oxidase and therefore displays cytochrome c oxidase activity. Apr 2, 2014 · The redox potential of the PQ pool is clamped by the relative rates of electron release into and uptake from this pool. 1). Q represents the ubiquinone form of CoQ, and QH 2 represents the ubiquinol (dihydroxyquinone) form. For example, the ArcB sensor kinase in E. Consequently, quinol oxidation would provide the electrons for hydrazine synthesis and nitrite reduction. Notably, under aerobic conditions, about 40% of the quinone pool was in the reduced state, while no reduced UQ was detected under anaerobic conditions. Schematic representation of complex III of the electron transport chain. The polymerization of the CoQ isoprenoid tail and the quinone head group modifications take place in a multiprotein complex of at least 12 proteins in MIM (reviewed in [[50]] and [[51]]). Oct 1, 2009 · Therefore, the predominance of one quinone structure (at a particular oxidation state) over another likely depends upon the rates of cross reactions and self-exchange reactions between fully oxidized and reduced forms within the quinone pool. 1 mol ubiquinone/mol cytochrome b-561 before the flash. coli consists of three quinone types, the benzoquinone ubiquinone (UQ) and the naphtoquinones demethylmenaquinone (DMK) and menaquinone (MK); for reviews, see (Unden and Bongaerts, 1997; Sharma et al. Nov 1, 2024 · The results are discussed in the framework of the current knowledge of protein organization and quinone pool reduction in bacterial photosynthetic membranes. Complex I (NADH:ubiquinone oxidoreductase) is the first enzyme of the respiratory Abstract Strong evidence for a random collisional mechanism for ubiquinone-mediated electron transfer is provided by the characteristic kinetic properties of respiratory chains originally explored by Kröger, A. b The Qo site becomes oxidized, transferring two protons across the membrane and Mar 17, 2003 · 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. , 2012), with on average a prenyl side-chain length of 8 (Meganathan, 2001b). Dec 1, 2020 · Plastoquinone-9 (PQ-9) is an essential component of photosynthesis that carries electrons in the linear and alternative electron transport chains, and is also a redox sensor that regulates state transitions and gene expression. AOX expression did not alter complex I abundance, supercomplexes assembly, or basal respiration rates, but effectively diverted electrons from the quinone pool, decreasing RET flux via complex I and limiting ROS 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 Roman Grabbe and Ruth A. The amount of each quinone species was calculated from the relevant area under the peak. The ubiquinone pool in photosynthetic bacteria may play a role in a O-type cycle as proposed by Mitchell24B (for basic me- chanism, see section III A). Throughout this document, the quinone redox state is defined by . However, the importance of quinone formation to the off-target effects of drugs, natural products, environmental chemicals, and xenobiotic/endogenous compounds in general is often underestimated. Sep 7, 2016 · The quinone pool of E. Nov 30, 2006 · The oxidation of H 2 S to thiosulfate by a model quinone Q, which is reduced to Q H 2 can be represented by (1) 4 Q + 2 H 2 S + 3 H 2 O → 4 Q H 2 + S 2 O 3 2 + 2 H + Incorporation of sulfur into the organic structure at reactive site X was accounted for as an additional, sulfide-consuming process. Meanwhile, quinone molecules are also considered a source of exogenous stress: a variety of toxins and antimicrobial compounds contain quinone, such as cercosporin and anthracycline (12 – 14). Jun 11, 2019 · In case that the quinone pool is predominantly reduced, it is not capable of oxidizing reduced N2. [6] The activity of Complex III is commonly assayed by monitoring the reduction of cytochrome c, which is dependent on A. D. At both potentials, cytochrome b-561 became completely reduced following one flash in the presence of antimycin. The bacterial quinone pool is the primary modulator of ArcAB activity, but questions remain for how this regulation occurs. 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. Dec 31, 2013 · Under anaerobic conditions where the chromatophores quinone pool is fully reduced, we deduce, on the basis of flash-induced fluorescence kinetics, that the reduced RCs are exclusively reoxidized by the quinone generated at the Q o site of the cyt bc 1 complex. Sep 9, 2008 · When the forward electron flow is blocked (completely reduced quinone pool) and Q A is in its normal low potential form, the back reaction via the primary radical pair (P 680 + Ph −) is favoured, leading to a higher probability of 3 P 680 and 1 O 2 formation. The MCAT (Medical College Admission Test) is offered by the AAMC and is a required exam for admission to medical schools in the USA and Canada. This review highlights the role of quinones and their oxidation state in activating and deactivating ArcB and compares competing models of the regulatory mechanism. Decylubiquinol, the reduced form of decylubiquinone, is an excellent substrate for Complex III. In addition, the value of the Km for oxygen varied with the redox poise of the ubiquinone pool, measured voltametrically; the more reduced the quinone pool, the larger the observed Km. Schematic representation of the Q-cycle as we think of it today in cytochrome bc1 (represented here as a monomer for simplicity). Following excitation of the reaction center by a photon, QI is reduced via an intermediary In the presence of a reduced Q pool and a sufficiently high membrane potential, complex I can reduce NAD + by reverse electron transfer (RET), e. Jul 1, 2025 · In this system, ArcB indirectly perceives the ambient oxygen concentration by directly sensing the redox state of the intima quinone pool [54]. These electron-transfer reactions may be summarized by t s, one pri-mary and the other secondary, acting in series. 5B). The reduced state of N2 leads to a reduction of N1a by FMNH* 21. The redox state of the Q pool correlates closely with the electron flux through the ETC and is thus a Jan 1, 2015 · These carriers form two redox pools, each confined to the environment of different polarity. The quinone pool of E. May 27, 1983 · 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]. In E. Aug 1, 1988 · It can be seen from fig. Dec 1, 2004 · This pool consists of oxidized (PQ) and reduced (PQH 2) plastoquinones (plastoquinone, rather than quinone, is specified when it is the predominant quinone). Feb 4, 2025 · Quantitative data on the reduction potentials and proton motive force (particularly the rhodoquinone pool potential) under different mitochondrial conditions will be essential to define the energetic landscape of rhodoquinone-mediated catalysis and understand the complex interplay of thermodynamics and kinetics in determining pathway fluxes. The system functioned with very low quinone concentrations because NOM was recycled by the nitroaromatic reduction. Jul 23, 2020 · Plastoquinone-9 (PQ-9) is an essential component of photosynthesis that carries electrons in the linear and alternative electron transport chains, and is also a redox sensor that regulates state transitions and gene expression. Nov 11, 2003 · An oxidized quinone derived from the quinone pool replaces the transient reduced quinone (step 1). The cytochrome bd complex allows oxygen to be reduced by the quinone pool. Apr 1, 2024 · It allows the determination of both reduced and oxidized quinone concentrations but gives a static idea of the quinone redox state as analyses are realized at a given time. At a quinone site towards one side of the membrane, quinone (Q) is reversibly and doubly reduced, picking up two protons in the process to form hydroquinone (QH 2). The grey area is the inner mitochondrial membrane. Jul 1, 2022 · In both Gram-negative and -positive species, the composition and/or redox state of the quinone pool can serve as a regulatory signal that controls important physiological processes. 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- and emission wavelength, respectively, with the photomultiplier gain set to 12. Jun 1, 2007 · 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. Yet it is convenient to discuss their chemistry at this point because quinones and the related aromatic arenols are readily interconverted, and their chemistry is largely interdependent. Post questions, jokes, memes Complex III (Cytochrome bc1 Complex) Complex III, also known as ubiquinol-cytochrome c reductase, accepts electrons from the reduced quinone pool and transfers them to cytochrome c. The reduced quinone, QH2, gives up two protons and one electron to form the semiquinone radical, Q. , refs. Jan 1, 2008 · However, in the absence of superoxide dismutase (SOD), quinone reduction by CBR1 leads to redox cycling, with generation of superoxide anion and semiquinone radicals mediated through one-electron transfer from the reduced hydroquinones to molecular oxygen (Jarabak and Harvey 1993). vinosum [25] it is a menaquinone, probably MK-7. Using quantum chemistry and electrostatic calculations, we have examined the pKa of the reduced quinone QH-/QH2 in the catalytic cavity of Thiosulfate respiration in Salmonella enterica serovar Typhimurium is catalyzed by the membrane-bound enzyme thiosulfate reductase. coli, for example, NDH-2 – a non-proton pumping NADH:quinone oxidoreductase – is a major contributor to both reduced quinone and superoxide 11, 12. Jan 1, 2012 · In the course of electron transport, the doubly reduced and doubly protonated mobile carrier PQH 2 has to be replaced from the Q B site by fresh PQ from the quinone pool located in the thylakoid membrane. Download scientific diagram | Photosystem II and ETC-related photochemical traits: (A) oxidized quinone pool; (B) reaction center turnover rate (N); (C) the energy needed to close all reaction Jan 12, 2021 · The reduced quinone pool provides electrons further to complex III (cytochrome bc1), from where the electrons continue via the soluble electron carrier cytochrome c (Em,7 = +250 mV) to terminal Nov 11, 2017 · The acyl-CoA dehydrogenases capture electrons extracted during β-oxidation of CoA-conjugated fatty acids or oxidation of amino acids. Sep 2, 2019 · Moreover, the rates of quinol oxidation and quinone reduction were equivalent, indicating that the quinone pool was more reduced when compared to the redox state during growth on acetate and butyrate. J. Each panel represents a step in the electron and/or proton transfer process of one complete Q-cycle. Possible mechanisms for energetic benefit from iron oxidation coupled to nitrate reduction. Apr 8, 1985 · Previous kinetic descriptions of Q-pool behaviour have assumed that productive collision between a quinone and a quinone-reactive enzyme determined the overall electron-transfer rate, and this has led to a widespread view that quinonemediated electron transfer is therefore controlled by the rate of quinone diffusion in the membrane. This increases the rate of the reaction through the second-order effect, and also reduces the lag. 9,10-Anthraquinone-2,7-disulphonic acid (AQDS) a quinone similar to one found naturally in rhubarb has been used as a charge carrier in metal-free flow batteries. Therefore, it predicts how fast ascorbate-driven redox cycling will generate hydrogen peroxide under a variety of conditions and with different quinones. Jun 18, 2018 · This suggests that the reaction is electrogenic and contributes to the membrane potential while also conserving energy by reducing the quinone pool. Sep 17, 2019 · Control samples with fully oxidized and reduced photoactive PQ pool were prepared by far-red and high light treatments, respectively, or by blocking the photosynthetic electron transfer chemically before or after PQ in moderate light. coli responds to the reduced quinone pool (Georgellis et al. Pool behaviour at the quinone reductase site The reduced form of the quinone can then react with other molecules, leading to the formation of new compounds. Q A is a one-electron carrier, whereas Q B undergoes sequential reduction and protonation to form Q B H 2. /r/MCAT is a place for MCAT practice, questions, discussion, advice, social networking, news, study tips and more. These changes appear to play a key role in the resulting inhibition of fatty acid oxidation and of mitochondrial oxidative-phosphorylation associated with an incre … For reduction of cyto-chrome c, the quinone-cycling mecha-nism of complex III requires both quinol and quinone, so switching to rhodoquinol may slow turnover (despite more favor-able overall thermodynamics) through lack of one of the substrates in a heavily oxidized or reduced pool and/or slow a potential-dependent step in quinone reduction. The landscape of quinone utilizing enzymes is broad, and we have selected a subset for review using several criteria. Abstract Purple bacteria have thus far been considered to operate light-driven cyclic electron transfer chains containing ubiquinone (UQ) as liposoluble electron and proton carrier. Our results are probably generally applicable to quinone redox regulation in bacteria. (1973), Eur. Sep 5, 2019 · Again, this fits qualitatively with the situation reported in purple bacterial reaction centers (39, 45). When E. Here, we describe the simultaneous A bacterial electron transport system is shown below. Plastoquinone, the major quinone in chloroplasts and cyanobacteria, is responsible for transporting redox forces between membrane complexes [84]. sphaeroides [15,46] and R. If the rates of N2 cluster oxidation are low due to a predominantly reduced quinone pool, this causes reduction of N1a by FMNH· and a conformational switch within the NADH binding pocket that favours NAD +. We show that in the purple γ-proteobacterium Halorhodospira halophila, menaquinone-8 (MK-8) is the dominant quinone component and that it operates in the Q B -site of the photosynthetic reaction center (RC). g. Check out the sidebar for useful resources & intro guides. nitroreducens, electrons from the reduced quinone pool may travel via the Rieske/cytb complex andthepentahemec-typecytochromestothepseudoperiplasmic space and at that place they may be used by the nitrate reductase to reduce the external electron acceptor nitrate. The ArcAB system senses the oxidation state of the membrane-localized quinone pool (72), indicating that HOCl treatment might have an effect on the ratio of reduced quinone to oxidized quinone. The redox state of the NDH1-complex would be reduced and the redox state of cytbo would be oxidized because the electron transport would be blocked at the quinone pool. , and Klingenberg, M. 34, 313-323. At values of Eh < 170 mV a significant fraction of the quinone pool is reduced before the flash. Jun 15, 2022 · The bacterial quinone pool is the primary modulator of ArcAB activity, but questions remain for how this regulation occurs. However, under conditions when reoxidation of flavin is slow (the presence of complex I inhibitors, a highly reduced quinone pool, or reverse electron transport), the rate of ROS production increases (39), consistent with our structural interpretation. The electrically neutral and non-polar QH 2 diffuses across the membrane to a second quinone site, at which QH 2 is reversibly and doubly oxidized to Q, releasing two protons. The Q cycle (named for quinol) describes a series of sequential oxidation and reduction of the lipophilic electron carrier Coenzyme Q (CoQ) between the ubiquinol and Feb 1, 2025 · A minimal respiratory chain was constructed with an excess of NADH and NDH-2, such that the quinone pool remains fully reduced. In the literature, it has often been assumed that the binding constants of the quinone and quinol in the Q B site are equal both in PSII and in purple bacterial reaction centers (e. Complex III of the electron transport chain, also known as Q-cytochrome c oxidoreductase or simply cytochrome reductase, is a multi-subunit structure that functions to accept electrons from ubiquinol and transfer them onto another electron carrier called cytochrome c. Nov 8, 2002 · Because this enzyme is not reducible with succinate, we prepared the enzyme in vesicles from strain KM31 (Δ (frdABCD) 18 sdhC4:: kanr katE katG14 pFRDA H44C) containing α-glycerolphosphate dehydrogenase, and we reduced the enzyme via the quinone pool, using α-glycerol phosphate as a respiratory substrate. Aug 1, 2021 · Since the strong the g x 1. 2B) and physiologically couples the reduction of ubiquinone to the oxidation of succinate, thus contributing to the formation of the reduced quinone pool. The quinone pool acts as the central hub for shuttling electrons between different respiratory proteins. 5 to 1 s (5) if the water-splitting complex is in state S 2 or S 3. 6 - 8 More particularly, they have also been extensively used as mediators in (bio)fuel cells applications or This oxidation of the high potential chain generated a system similar to that used as the starting point in experiments with the isolated mi-tochondrial complex (the fully oxidized complex), except that QH2 was available immediately in the partly reduced quinone pool of the chromatophore membrane. There is no correlation between the redox potentials of the quinone and pyridine nucleotide pools. The electron in step three goes over to reduce ferric ion to ferrous iron, that is iron three to iron two in cytochrome c. We show how wavelengths and intensity of photosynthe Simple Q-Pool Behavior Inasystem in which quinone acts a a freely andrapidly diffusing entity linking reductases with oxidases, which are themselves randomly diffusing in the membrane, it follows that electrons donated into he quinone pool by any one quinone reductase molecule anb withdrawn with equal probability y any quinol oxidase molecule. ) that in the presence of succinate as an oxidisable substrate, under state 4 conditions, the quinone pool is 85% reduced and that progressive inhibition of the input of reducing 79 Volume 235, number 1,2 FEBS LETTERS August 1988 equivalents from complex 2 results in the net oxidation of quinone. Hence, AOX represents a natural rescue mechanism from respiratory stress. In Rp. Step-by-step explanation 13. The redox state of the Q pool correlates closely with the electron flux through the ETC and is thus a parameter of great metabolic value for both the mitochondrial and cellular metabolism. Oct 1, 2016 · Regarding energy conservation, it is thought that the (four) electrons that originate from hydrazine oxidation feed the reduced quinone (quinol, Q-) pool by the action of an as yet-unknown oxidoreductase (Fig. , during reperfusion after ischemia (Chouchani et al. Schmitz Institut fu ̈r Mikrobiologie und Genetik, Georg-August Universita ̈t Go ̈ttingen, Germany Quinone function is the characteristic that distinguishes between type I reaction centers where bound quinone is only transiently reduced to semiquinone and type II reaction centers where quinone is doubly reduced to QH 2 and released to the membrane Q pool (Heathcote 2002). 18 and 20). May 19, 2025 · This enzyme bypasses complexes III and IV by directly oxidizing the reduced quinone pool and passing electrons onto molecular oxygen. We detect differences in the currents produced by CI and CII activities, in agreement with models that suggest that supercomplexes play a role in regulating the spatial distribution of the reduced quinone. In the second step, the semiquinone is reduced into a quinone dianion. Hill function analysis of the photosynthetic membrane induction in response to the quinone redox state suggests that the induction process is highly cooperative. Jan 30, 2019 · Tuning the reduction potential of quinones by controlling the effects of hydrogen bonding, protonation and proton-coupled electron transfer reactions †. The two-electron reduction of the secondary quinone results from two one-electron reduct Aug 24, 2021 · The mitochondrial CoQ pool can be compromised by defects in the biosynthesis of CoQ or due to a blockade in ETS upstream of CoQ. The resident reduced quinone transfers electrons to the transient quinone through a quinhydrone complex, as shown at the top. 800 signal was seen only when ISP was reduced and the quinone pool oxidized, we suggested that the simplest interpretation was that it represented a complex between the reduced ISP and ubiquinone (Q) through the same His-161 as seen in the stigmatellin complex [127], but with relatively weak binding. C. Quinone redox cycling refers to the repeated oxidation and reduction of quinones, which can generate reactive oxygen species (ROS). , 2001). minus. One pool, formed by quinone molecules (the Q pool), is confined to the lipid phase of inner mitochondrial membrane while the second pool, formed by cytochrome c (the C pool), is confined to the water phase of mitochondrial intermembrane space. Feb 4, 2025 · For reduction of cytochrome c, the quinone-cycling mechanism of complex III requires both quinol and quinone, so switching to rhodoquinol may slow turnover (despite more favorable overall thermodynamics) through lack of one of the substrates in a heavily oxidized or reduced pool and/or slow a potential-dependent step in quinone reduction. Dec 31, 2012 · PQ reduction involves two PQ cofactors, Q A and Q B, working in series. The molecules were generated as fully reduced parts of redox pairs and subject to two-proton, two-electron oxidation reactions. Subunit a of the F-type ATPase has 876 amino acids. Control studies with varying amounts of NDH2 confirmed that cyt bd activity was limiting. Jan 1, 1986 · For bacterial photosynthesis under conditions where single turnovers are induced, for example by single light flashes, only the primary and secondary quinone acceptors appear to be requi- red. The photoactive pool comprised 50% of total PQ. The Sep 19, 2003 · With the quinone pool partly reduced, the phase of re-reduction kinetics because of oxidation of QH 2 in the bifurcated reaction becomes rapid enough to truncate the oxidative phase, but a rate of reduction of cyt c 1, which is slower than the rate in the presence of myxothiazol, is still apparent in the 100–500-μs range (Fig. As I mentioned earlier, cytochrome c is another one of our mobile electron carriers. 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. With the quinone pool partly reduced, the phase of re-reduction kinetics because of oxidation of QH 2 in the bifurcated reaction becomes rapid enough to truncate the oxidative phase, but a rate of reduction of cyt c 1, which is slower than the rate in the presence of myxothiazol, is still apparent in the 100–500-μs range (Fig. Mar 11, 2013 · A disordered quinone pool would severely affect the respiratory systems of Drosophila, leading to subsequent changes in cellular metabolism (9 – 11). Aug 31, 2017 · To extend the analogy between quinones and MPh, we compared the MPh pool sizes between two well-studied Methanosarcina species, Methanosarcina acetivorans C2A and Methanosarcina barkeri Fusaro, to the quinone pool size in the bacterium Escherichia coli. Jun 24, 2023 · 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 and non-enzyme inhibitions. [6–8]More particularly, they have also been extensively used as mediators in (bio)fuel cells applications or These carriers form two redox pools, each con-fined to the environment of different polarity. Biophys. A kinetic model which leads to this so-called "simple Q-pool behavior" has been described and we use this in reviewing Jun 24, 2023 · 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 and non-enzyme inhibitions. In this chapter we discuss the electron-transfer reactions between Qa and Qb, exchange between reduced Qb and the quinone pool, and protonation coupled to electron transfer. Apr 1, 1998 · All of the incorporated quinone species can be reduced or oxidized at the built-in gold electrode. For PSII to function optimally, it makes sense that the binding of the substrate (the quinone) is favored over that of the product (the quinol). Schmitz Institut fu ̈r Mikrobiologie und Genetik, Georg-August Universita ̈t Go ̈ttingen, Germany Aug 18, 2020 · Our results suggest that quinone binding and chemistry play a key role in the coupling mechanism of complex I. In M. The purpose of this vicious cycle is to avoid excessive ROS production that would be deleterious to cell survival. Mitochondrial complex I from many species can switch reversibly from an active A-form to a deactive D-form (Kotlyar and Vinogradov, 1990). Thus, the quinone respiration expanded the spectrum of nitroaromatics susceptible to transformation. Quinone function is the characteristic that distinguishes between type I reaction centers where bound quinone is only transiently reduced to semiquinone and type II reaction centers where quinone is doubly reduced to QH 2 and released to the membrane Q pool (Heathcote 2002). , 2014). Q B H 2 exchanges with PQ from the pool in the membrane. This is contrary to expectation. ulzf yscadsz vodq efrdqk cte qgpwio krnk wiqcyd gsf byn xdhegi roq jxdb cbevoly zbkku