Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Succinates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources
PubMed1988

Pathways of succinate formation and their contribution to improvement of cardiac function in the hypoxic rat heart.

Hypoxia led to a dramatic acceleration of amino acid breakdown together with succinate synthesis in the rat heart. Our data do not confirm the simultaneous conversion of aspartate and glutamate to succinate, which has been repeatedly assumed in the literature (7, 8, 21, 28-30), but rather suggest that different pathways are involved during developing hypoxia and that glutamate is the sole source for anaerobic succinate production from endogenous sources in the glucose-perfused heart. Perfusion of hypoxic rat hearts with 2-oxoglutarate, malate, and fumarate (5 mM each) increased succinate formation three- to fourfold. The beneficial effects of these substances on left ventricular systolic pressure, end diastolic pressure, and time of recovery may be due to the elevated content of ATP in these hearts compared to hypoxic controls with glucose as the sole substrate. However, the maintenance of a high rate of anaerobic glycolysis in hearts perfused with 2-oxoglutarate, malate, and fumarate and not the small stimulation of succinate synthesis is considered to be the most important mechanism of cardiac protection. A proposed pathway assumes that malate, after dehydration to fumarate, may serve as an alternative electron acceptor for cytosolic NADH during conditions of oxygen deficiency, thereby cancelling glycolytic inhibition.

Amino Acids↗
PubMed2005

Development of a solid-phase extraction/gas chromatographic-mass spectrometric method for quantification of succinic acid in nucleoside derivatives for oligonucleotide synthesis.

A solid-phase extraction (SPE)/gas chromatographic-mass spectrometric (GC-MS) method was developed for analysing residual succinic acid in nucleoside derivatives to be used in oligonucleotide synthesis. Use of a SPE protocol, enabled most of the derivatives to be trapped, thereby creating eluates enriched in succinic acid. GC-MS was used to quantify the amount of residual succinic acid in four different nucleoside preparations, with succinate concentrations varying from 0.18 to 0.24% (w/w). The within-day repeatability of the method was found to be 1.25% RSD. A linear relationship was observed between the amount of succinic acid in the sample and the GC-MS peak area, with a correlation coefficient of 0.9997 in the concentration interval 0.05-2.5% (w/w). Recoveries were measured by the addition of internal standards to working solutions and varied between 99.8 and 102.6%.

Chromatography, Liquid↗
PubMed2006

Nonezymatic formation of succinate in mitochondria under oxidative stress.

The products of the reactions of mitochondrial 2-oxo acids with hydrogen peroxide and tert-butyl hydroperoxide (tert-BuOOH) were studied in a chemical system and in rat liver mitochondria. It was found by HPLC that the decarboxylation of alpha-ketoglutarate (KGL), pyruvate (PYR), and oxaloacetate (OA) by both oxidants results in the formation of succinate, acetate, and malonate, respectively. The two latter products do not metabolize in rat liver mitochondria, whereas succinate is actively oxidized, and its nonenzymatic formation from KGL may shunt the tricarboxylic acid (TCA) cycle upon inactivation of alpha-ketoglutarate dehydrogenase (KGDH) under oxidative stress, which is inherent in many diseases and aging. The occurrence of nonenzymatic oxidation of KGL in mitochondria was established by an increase in the CO(2) and succinate levels in the presence of the oxidants and inhibitors of enzymatic oxidation. H(2)O(2) and menadione as an inductor of reactive oxygen species (ROS) caused the formation of CO(2) in the presence of sodium azide and the production of succinate, fumarate, and malate in the presence of rotenone. These substrates were also formed from KGL when mitochondria were incubated with tert-BuOOH at concentrations that completely inhibit KGDH. The nonenzymatic oxidation of KGL can support the TCA cycle under oxidative stress, provided that KGL is supplied via transamination. This is supported by the finding that the strong oxidant such as tert-BuOOH did not impair respiration and its sensitivity to the transaminase inhibitor aminooxyacetate when glutamate and malate were used as substrates. The appearance of two products, KGL and fumarate, also favors the involvement of transamination. Thus, upon oxidative stress, nonenzymatic decarboxylation of KGL and transamination switch the TCA cycle to the formation and oxidation of succinate.

Amination↗
PubMed2003

Growth-related changes in cell body size and succinate dehydrogenase activity of spinal motoneurons innervating the rat soleus muscle.

Cell body sizes and oxidative enzyme (succinate dehydrogenase) activities of spinal motoneurons innervating the soleus muscle were determined in rats ranging in postnatal age from 3 to 13 weeks. The soleus motoneurons were labeled by a retrograde neuronal tracer, nuclear yellow. The mean cell body sizes of motoneurons increased from 3 to 7 weeks of age, while the mean succinate dehydrogenase activities of motoneurons decreased from 3 to 7 weeks of age. There were no changes in mean cell body size or mean succinate dehydrogenase activity of motoneurons from 7 to 13 weeks of age. An inverse relationship between cell body size and succinate dehydrogenase activity of motoneurons was observed, irrespective of age. These results indicate that motoneurons innervating the rat soleus muscle show the adult pattern of cell body size and succinate dehydrogenase activity at an earlier stage of postnatal growth, 7 weeks of age.

Aging↗
PubMed2003

Anxiolytic-like effect of succinic acid in mice.

The putative anxiolytic activity of succinic acid was examined in male mice by using a number of experimental paradigms of anxiety and compared with that of the known anxiolytic compound diazepam. Use of the elevated plus-maze test revealed that diazepam (1.0, 2.0 and 4.0 mg/kg, PO) or succinic acid (3.0 or 6.0 mg/kg, PO) increased the percentage of entries into open arms and of time spent on open arms. In novel food consumption test, succinic acid (3.0, 6.0, and 12.0 mg/kg, IP) caused significant increases in food intake during 5 min when compared with the vehicle. In the stress-induced hyperthermia test, 40 min after drug administration rectal temperature was measured, succinic acid at dose of 1.5 mg/kg, inhibited stress-induced hyperthermia. Thus, these findings indicated that, in contrast with diazepam, succinic acid exhibits anxiolytic-like effect.

Animals↗
PubMed2005

Succinate and artificial maintenance of normal body temperature synergistically correct lethal disorders in thiopental coma rat.

Under modeling of thiopental coma influence of sodium succinate and (or) external warming for the support of normal body temperature (isothermal regimen) on the gas exchange, blood gas content, acid-base status and survival rate was studied in rats. In the absence of therapy hypothermia was developed (-9.4 degrees C), O(2) consumption decreased by a factor 5, oxygenation of arterial blood (pO(2)) did not change while that of venous blood increased, where with arteriovenous oxygen tension gradient decreased by half. Blood tension of carbon dioxide (pCO(2)) increased twice, respiratory and metabolic acidosis was developed. Survival rate under absence of a therapy was 42%, with isolated use of isothermal regimen or succinate therapy alike-50%; with their use in combination drastically increased up to 92%. Succinate increased arteriovenous gradient of pO(2), decreased deficit of buffer bases, increased bicarbonate concentration. At isothermal regimen accumulation of CO(2) in the blood was diminished, its excretion was increased, pH of blood approached normal values. Combined use of both therapy agents increased O(2) consumption and potentiated their positive influence on acid-base status. The implication is that hypothermia restrains effect of succinate in barbiturate coma; prevention of hypothermia in combination with succinate administration is highly effective method of experimental therapy of barbiturate intoxication.

Anesthetics, Intravenous↗
PubMed2005

Chemostat culture characterization of Escherichia coli mutant strains metabolically engineered for aerobic succinate production: a study of the modified metabolic network based on metabolite profile, enzyme activity, and gene expression profile.

Various Escherichia coli mutant strains designed for succinate production under aerobic conditions were characterized in chemostat. The metabolite profiles, enzyme activities, and gene expression profiles were studied to better understand the metabolic network operating in these mutant strains. The most efficient succinate producing mutant strain HL27659k was able to achieve a succinate yield of 0.91 mol/mol glucose at a dilution rate of 0.1/h. This strain has the five following mutations: sdhAB, (ackA-pta), poxB, iclR, and ptsG. Four other strains involved in this study were HL2765k, HL276k, HL2761k, and HL51276k. Strain HL2765k has mutations in sdhAB, (ackA-pta), poxB and iclR, strain HL276k has mutations in sdhAB, (ackA-pta) and poxB, strain HL2761k has mutations in sdhAB, (ackA-pta), poxB and icd, and strain HL51276k has mutations in iclR, icd, sdhAB, (ackA-pta) and poxB. Enzyme activity data showed strain HL27659k has substantially higher citrate synthase and malate dehydrogenase activities than the other four strains. The data also showed that only iclR mutation strains exhibited isocitrate lyase and malate synthase activities. Gene expression profiles also complemented the studies of enzyme activity and metabolites from chemostat cultures. The results showed that the succinate synthesis pathways engineered in strain HL27659k were highly efficient, yielding succinate as the only major product produced under aerobic conditions. Strain HL27659k was the only strain without pyruvate accumulation, and its acetate production was the least among all the mutant strains examined.

Aerobiosis↗
PubMed1999

The unusual iron sulfur composition of the Acidianus ambivalens succinate dehydrogenase complex.

The succinate dehydrogenase complex of the thermoacidophilic archaeon Acidianus ambivalens was investigated kinetically and by EPR spectroscopy in its most intact form, i.e., membrane bound. Here it is shown that this respiratory complex has an unusual iron-sulfur cluster composition in respect to that of the canonical succinate dehydrogenases known. The spectroscopic studies show that center S3, the succinate responsive [3Fe-4S]1+/0 cluster of succinate dehydrogenases, is not present in membranes prepared from aerobically grown A. ambivalens, nor in partially purified complex fractions. On the other hand, EPR features associated to the remaining centers, clusters S1 ([2Fe-2S]1+/2+) and S2 ([4Fe-4S]2+/1+), could be observed. Similar findings were made in other archaea, namely Acidianus infernus and Sulfolobus solfataricus. Kinetic investigations showed that the A. ambivalens enzyme is reversible, capable of operating as a fumarate reductase - a required activity if this obligate autotroph performs CO2 fixation via a reductive citric acid cycle. Sequencing of the sdh operon confirmed the spectroscopic data. Center S3 ([3Fe-4S]) is indeed replaced by a second [4Fe-4S] center, by incorporation of an additional cysteine, at the cysteine cluster binding motif (CxxYxxCxxxC-->CxxCxxCxxxC). Genomic analysis shows that genes encoding for succinate dehydrogenases similar to the ones here outlined are also present in bacteria, which may indicate a novel family of succinate/fumarate oxidoreductases, spread among the Archaea and Bacteria domains.

Amino Acid Sequence↗
PubMed1999

Voltammetric studies of bidirectional catalytic electron transport in Escherichia coli succinate dehydrogenase: comparison with the enzyme from beef heart mitochondria.

The succinate dehydrogenases (SDH: soluble, membrane-extrinsic subunits of succinate:quinone oxidoreductases) from Escherichia coli and beef heart mitochondria each adsorb at a pyrolytic graphite 'edge' electrode and catalyse the interconversion of succinate and fumarate according to the electrochemical potential that is applied. E. coli and beef heart mitochondrial SDH share only ca. 50% homology, yet the steady-state catalytic activities, when measured over a continuous potential range, display very similar catalytic operating potentials and energetic biases (the relative ability to catalyse succinate oxidation vs. fumarate reduction). Importantly, E. coli SDH also exhibits the interesting 'tunnel-diode' behaviour previously reported for the mitochondrial enzyme. Thus as the potential is lowered below ca. -60 mV (pH 7, 38 degrees C) the rate of catalytic fumarate reduction decreases abruptly despite an increase in driving force. Since the homology relates primarily to residues associated with active site regions, the marked similarity in the voltammetry reaffirms our previous conclusions that the tunnel-diode behaviour is a characteristic property of the enzyme active site. Thus, succinate dehydrogenase is an excellent fumarate reductase, but its activity in this direction is limited to a very specific range of potential.

Amino Acid Sequence↗
PubMedDate not supplied

Streptavidin in antibody pretargeting. 3. Comparison of biotin binding and tissue localization of 1,2-cyclohexanedione and succinic anhydride modified recombinant streptavidin.

Recombinant streptavidin (rSAv) is of interest as a carrier of alpha-emitting radionuclides in pretargeting protocols for cancer therapy. Due to the inherently high kidney localization of rSAv, modification of this protein is required before it can be useful in pretargeting. Previous studies (Wilbur, D. S., Hamlin, D. K. et al. (1998) Bioconjugate Chem. 9, 322-330) have shown that succinylation of rSAv using succinic anhydride decreases the kidney localization appreciably. In continuing studies, the biotin binding characteristics and biodistribution in mice of rSAv modified by reaction with succinic anhydride (amine modification) or 1,2-cyclohexanedione (arginine modification) have been compared. Modification of rSAv was conducted using 5-50 mol equiv of succinic anhydride and 60-200 mol equiv of 1,2-cyclohexanedione. Most studies were conducted using rSAv modified with the highest quantities of reagents. Succinylation of rSAv did not alter binding with biotin derivatives, but a small increase in the biotin derivative dissociation rate was noted for arginine-modified rSAv. Amino acid analysis of 1,2-cyclohexanedione-treated rSAv indicated about 40% of the arginine residues, or an average of 1.6 residues per subunit, were modified, whereas none of the lysine residues were modified. IEF analyses showed that the pI of the arginine-modified rSAv was 5.3-6, whereas the pI for the succinylated rSAv was approximately 4. Electrospray mass spectral analyses indicated that one to three conjugates of 1,2-cyclohexanedione, and two to three conjugates of succinic anhydride, were obtained per subunit. Both modification reactions resulted in greatly decreasing the kidney localization of rSAv (normally 20-25% ID/g at 4, 24, and 48 h pi). However, the kidney concentration for the succinylated rSAv continued to decrease (5% ID/g to 1.5% ID/g) from 4 to 48 h pi, whereas the concentration (5% ID/g) remained constant over that period of time for the arginine-modified rSAv. In contrast to this, the liver concentration appeared to be slightly higher (3% ID/g vs 2% ID/g) at the later time points for the succinylated rSAv. When less than 50 mol equiv of succinic anhydride were employed in the modification of rSAv, a correlation between increasing kidney localization with decreasing equivalents reacted was observed. Although the differences in the two modified rSAv are not substantial, succinylated rSAv appears to have more favorable properties for pretargeting studies.

Animals↗
PubMed1981

Interaction of succinate--ubiquinone reductase (complex II) with (arylazido)phospholipids.

The interaction of purified succinate dehydrogenase and succinate--ubiquinone reductase (complex II) with lipids was explored by using two (arylazido)phospholipids, one with the reactive nitrene in the head-group region of the bilayer [1-palmitoyl-2-(2-azido-4-nitrobenzoyl)-sn-glycero-3-[3H]phosphocholine (PLII)] and one with the nitrene on the methyl terminus of one of the fatty acid chains [1-myristoyl-2-[12-[(2-azido-4-nitrophenyl)amino]lauroyl]-sn-glycero-3-[14C]phosphocholine (PLI)]. Protein was reacted with vesicles of egg lecithin containing radioactive (arylazido)-phospholipids and the covalent cross-linking of lipid and protein induced by irradiation under UV light. Purified succinate dehydrogenase was found to bind to lipid vesicles through both subunits as both were labeled by PLII. The smaller subunit was inserted into the interior of the bilayer and labeled by PLI. Complex II was found to interact with lipid vesicles, with the smaller subunit of succinate dehydrogenase, CII-3, and CII-4 all inserted into the interior of the bilayer. The large subunit of succinate dehydrogenase was found to be held above the bilayer in complex II and not labeled by either probe. Results are used to derive a picture of the arrangement of subunits in complex II and to evaluate the utility of (arylazido)-phospholipids in membrane studies.

Affinity Labels↗
PubMedDate not supplied

Kinetics of the extraction of succinic acid with tri-n-octylamine in 1-octanol solution.

Kinetic studies for the extraction of succinic acid from aqueous solution with 1-octanol solutions of tri-n-octylamine (TOA) were carried out using a stirred cell with a microporous hydrophobic membrane. The interfacial concentrations of species were correlated and thus the intrinsic kinetics was obtained. The overall extraction process was controlled by the chemical reaction at or near the interface between the aqueous and organic phases. The formation reaction of succinic acid-TOA complex was found to be first order with respect to the concentration of succinic acid in the aqueous phase and the order of 0.5 with respect to that of TOA in the organic phase with a rate constant of (3.14 +/- 0.6) x 10(-8) m(2.5) x mol(-0.5) x s(-1). The dissociation reaction of succinic acid-TOA complex was found to be the second-order with respect to that of succinic acid-TOA complex in the organic phase and the order of -2 with respect to that of TOA in the organic phase with a rate constant of (1.44 +/- 1.4) x 10(-4) mol x m(-2) x s(-1).

1-Octanol↗
PubMed2001

Activation and inhibition of succinate-dependent Ca2+ transport in liver mitochondria during adaptation.

Succinate-dependent Ca2+ accumulation was investigated in rat liver mitochondria and in operation biopsies of patients under states either with prevalence of adrenergic influences (administration of activating doses of adrenaline, acute phase of immobilization stress, initial period after allogenic transplantation, and acute phase of myocardial infarction) or with prevalence of the reciprocal mediator acetylcholine (late period after transplantation, chronic ulcer disease of stomach and duodenum). Adrenaline prevalence leads to increase of succinate-dependent ATP synthesis and Ca2+ accumulation, which is due to known activation of succinate oxidation. However, together with activation, inhibition of these processes was revealed. The inhibition phase prevails under chronic pathology. Therefore, reciprocal regulation of succinate oxidation and succinate-dependent Ca2+ transport in mitochondria occurs in the body in the course of adaptation. The reciprocal regulation of mitochondrial processes is considered as a mechanism of reciprocal regulation of physiological functions.

Acute Disease↗
PubMed2001

The succinate dehydrogenase from the thermohalophilic bacterium Rhodothermus marinus: redox-Bohr effect on heme bL.

The succinate dehydrogenase from the thermohalophilic bacterium Rhodothermus marinus is a member of the succinate:menaquinone oxidoreductases family. It is constituted by three subunits with apparent molecular masses of 70, 32, and 18 kDa. The optimum temperature for succinate dehydrogenase activity is 80 degrees C, higher than the optimum growth temperature of R. marinus, 65 degrees C. The enzyme shows a high affinity for both succinate (Km = 0.165 mM) and fumarate (Km = 0.10 mM). It contains the canonical iron-sulfur centers S1, S2, and S3, as well as two B-type hemes. In contrast to other succinate dehydrogenases, the S3 center has an unusually high reduction potential of +130 mV and is present in two different conformations, one of which presents an unusual EPR signal with g values at 2.035, 2.009, and 2.001. The apparent midpoint reduction potentials of the hemes, +75 and -65 mV at pH 7.5, are also higher than those reported for other enzymes. The heme with the lower potential (heme bL) presents a considerable dependence of the reduction potential with pH (redox-Bohr effect), having a pKa(OX) = 6.5 and a pKa(red) = 8.7. This behavior is consistent with the proposal that in these enzymes menaquinone reduction occurs close to heme bL, near to the periplasmic side of the membrane, and involving dissipation of the proton transmembrane gradient.

Amino Acid Sequence↗
PubMed2000

Autoantibodies to the flavoprotein subunit of succinate dehydrogenase: analysis of specificity in autoimmune thyroid disease.

OBJECTIVE: Thyroid-associated ophthalmopathy is a progressive eye disorder affecting the extraocular muscle and orbital connective tissue and is considered to have an autoimmune aetiology. A recent study reported a close relationship between serum antibodies against the flavoprotein subunit of succinate dehyhdrogenase (SDHFp) and active thyroid-associated ophthalmopathy involving eye muscle damage. The aim of the present study was to develop a sensitive and quantitative radiobinding assay for the detection of antibodies to the flavoprotein subunit of succinate dehydrogenase and to use this to determine the distribution of antibodies in different patient groups. DESIGN AND PATIENTS: Serum samples from the following patient groups were analysed: 20 systemic lupus erythematosus; 20 Addison's disease; 26 autoimmune hypothyroidism; 28 Graves' hyperthyroidism; 12 pretibial myxoedema; 25 thyroid-associated ophthalmopathy. Sera from 20 healthy subjects were used as controls. [35S]-labelled succinate dehydrogenase flavoprotein was produced in an in vitro transcription-translation system and subsequently used in immunoprecipitation experiments with sera from patient and control groups to test for the presence of antibodies to the flavoprotein. RESULTS: Succinate dehydrogenase flavoprotein antibodies were detected in five of the 20 (25%) patients with Addison's disease, six of the 20 (30%) with systemic lupus erythematosus, five of the 26 (19%) with autoimmune hypothyroidsm, six of the 28 (21%) with Graves' hyperthyroidism, two of the 12 (17%) with pretibial myxoedema and three of the 25 (12%) with thyroid-associated ophthalmopathy. The frequencies of flavoprotein antibodies were significantly greater than controls (P-value < 0.05) for patients with systemic lupus erythematosus (P = 0.02), but not for patients with either Addison's disease (P = 0.05), pretibial myxoedema (P = 0.13), Graves' hyperthyroidism (P = 0.07), autoimmune hypothyroidism (P = 0.06) or thyroid-associated ophthalmopathy (P = 0.24). For the patients with thyroid-associated ophthalmopathy, the frequency of SDHFp antibodies did not appear to be related to the length of time from diagnosis: the group containing samples taken less than one year from diagnosis showed no increased frequency of SDHFp antibodies when compared to controls (P = 0.10), with three of the 18 (17%) patients being positive. With respect to seven patients with thyroid-associated ophthalmopathy diagnosed for more than a year, SDHFp antibodies were not detected in any of their serum samples. In addition, the clinical severity of the disease, as recorded by the NOSPECS classification, did not correlate with the frequency of SDHFp antibodies: P = 0.13, 0.33 and 0.38, respectively, for patients with Grade II, III and IV ophthalmopathy. Similar results were also found in the case of patients with pretibial myxoedema and eye disease: P = 0.06 for patients with Grade III ophthalmopathy and, SDHFp antibodies were not detected in any of the sera taken from patients with Grade IV ophthalmopathy. In addition, no association was found between disease duration and the frequency of antibodies to the flavoprotein in this patient group. CONCLUSIONS: Our results indicate that succinate dehydrogenase flavoprotein antibodies are not a suitable marker for thyroid-associated ophthalmopathy, at least with the assay system used, as they can be found in patients who do not have eye disease and therefore lack the disease specificity required of a diagnostic tool.

Addison Disease↗
PubMed1998

Menaquinone-dependent succinate dehydrogenase of bacteria catalyzes reversed electron transport driven by the proton potential.

Succinate dehydrogenases from bacteria and archaea using menaquinone (MK) as an electron acceptor (succinate/menaquinone oxidoreductases) contain, or are predicted to contain, two heme-B groups in the membrane-anchoring protein(s), located close to opposite sides of the membrane. All succinate/ubiquinone oxidoreductases, however, contain only one heme-B molecule. In Bacillus subtilis and other bacteria that use MK as the respiratory quinone, the succinate oxidase activity (succinate-->O2), and the succinate/menaquinone oxidoreductase activity were specifically inhibited by uncoupler (CCCP, carbonyl cyanide m-chlorophenylhydrazone) or by agents dissipating the membrane potential (valinomycin). Other parts of the respiratory chains were not affected by the agents. Succinate oxidase or succinate/ubiquinone oxidoreductase from bacteria using ubiquinone as an acceptor were not inhibited. We propose that the endergonic electron transport from succinate (Eo' = +30 mV) to MK (Eo' approximately/= -80 mV) in succinate/menaquinone oxidoreductase includes a reversed electron transport across the cytoplasmic membrane from the inner (negative) to the outer (positive) side via the two heme-B groups. The reversed electron transport is driven by the proton or electrical potential, which provides the driving force for MK reduction.

Bacteria↗
PubMed2001

Generation of a proton potential by succinate dehydrogenase of Bacillus subtilis functioning as a fumarate reductase.

The membrane fraction of Bacillus subtilis catalyzes the reduction of fumarate to succinate by NADH. The activity is inhibited by low concentrations of 2-(heptyl)-4-hydroxyquinoline-N-oxide (HOQNO), an inhibitor of succinate: quinone reductase. In sdh or aro mutant strains, which lack succinate dehydrogenase or menaquinone, respectively, the activity of fumarate reduction by NADH was missing. In resting cells fumarate reduction required glycerol or glucose as the electron donor, which presumably supply NADH for fumarate reduction. Thus in the bacteria, fumarate reduction by NADH is catalyzed by an electron transport chain consisting of NADH dehydrogenase (NADH:menaquinone reductase), menaquinone, and succinate dehydrogenase operating in the reverse direction (menaquinol:fumarate reductase). Poor anaerobic growth of B. subtilis was observed when fumarate was present. The fumarate reduction catalyzed by the bacteria in the presence of glycerol or glucose was not inhibited by the protonophore carbonyl cyanide m-chlorophenyl hydrazone (CCCP) or by membrane disruption, in contrast to succinate oxidation by O2. Fumarate reduction caused the uptake by the bacteria of the tetraphenyphosphonium cation (TPP+) which was released after fumarate had been consumed. TPP+ uptake was prevented by the presence of CCCP or HOQNO, but not by N,N'-dicyclohexylcarbodiimide, an inhibitor of ATP synthase. From the TPP+ uptake the electrochemical potential generated by fumarate reduction was calculated (Deltapsi = -132 mV) which was comparable to that generated by glucose oxidation with O2 (Deltapsi = -120 mV). The Deltapsi generated by fumarate reduction is suggested to stem from menaquinol:fumarate reductase functioning in a redox half-loop.

Bacillus subtilis↗
PubMed1997

Electron paramagnetic resonance studies of succinate:ubiquinone oxidoreductase from Paracoccus denitrificans. Evidence for a magnetic interaction between the 3Fe-4S cluster and cytochrome b.

Electron paramagnetic resonance (EPR) studies of succinate:ubiquinone oxidoreductase (SQR) from Paracoccus denitrificans have been undertaken in the purified and membrane-bound states. Spectroscopic "signatures" accounting for the three iron-sulfur clusters (2Fe-2S, 3Fe-4S, and 4Fe-4S), cytochrome b, flavin, and protein-bound ubisemiquinone radicals have been obtained in air-oxidized, succinate-reduced, and dithionite-reduced preparations at 4-10 K. Spectra obtained at 170 K in the presence of excess succinate showed a signal typical of that of a flavin radical, but superimposed with another signal. The superimposed signal originated from two bound ubisemiquinones, as shown by spectral simulations. Power saturation measurements performed on the air-oxidized enzyme provided evidence for a weak magnetic dipolar interaction operating between the oxidized 3Fe-4S cluster and the oxidized cytochrome b. Power saturation experiments performed on the succinate- and dithionite-reduced forms of the enzyme demonstrated that the 4Fe-4S cluster is coupled weakly to both the 2Fe-2S and the 3Fe-4S clusters. Quantitative interpretation of these power saturation experiments has been achieved through redox calculations. They revealed that a spin-spin interaction between the reduced 3Fe-4S cluster and the cytochrome b (oxidized) may also exist. These findings form the first direct EPR evidence for a close proximity (</=2 nm) of the high potential 3Fe-4S cluster, situated in the succinate dehydrogenase part of the enzyme, and the low potential, low spin b-heme in the membrane anchor of the enzyme.

Cytochrome b Group↗