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PubMed1995

Influence of calcium on NADH and succinate oxidation by rat heart submitochondrial particles.

Physiological increases in matrix calcium are known to stimulate three mitochondrial dehydrogenases. In mitochondria isolated from rat heart, calcium stimulates rates of State 3 respiration during oxidation of succinate and of several NAD-linked substrates. In this study, we investigated the effects of calcium on NADH dehydrogenase and succinate dehydrogenase activities since the mechanism of these effects is unresolved. The respiratory activities of intact mitochondria and submitochondrial particles (SMP) were compared during incubation in media containing either ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) or a Ca2+/EGTA buffer (approximately 1 microM free Ca2+). In intact mitochondria oxidizing 20 mM glutamate plus 2 mM malate, the membrane potential (delta psi) and matrix NAD(P)H were maintained at higher levels, and the maximal rate of ADP-stimulated respiration (State 3) was increased twofold by the presence of calcium. With succinate as substrate, calcium stimulated State 3 respiration but it did not influence the pyridine nucleotides redox state or membrane potential. Stimulation of succinate-supported respiration by addition of 6-10 microM ADP in the presence of hexokinase caused a sudden decrease in NAD(P)H and collapse of delta psi. This effect was not caused by inhibition of succinate dehydrogenase or by opening of the nonspecific pore. Calcium did not influence the oxidation of succinate by SMP containing either activated or nonactivated succinate dehydrogenase. In addition, calcium did not alter the kinetics of succinate dehydrogenase activation. Calcium and magnesium, in the concentration range of 0.02 to 5 mM, did not influence the NADH dehydrogenase activity of SMP. Energization of SMP by oligomycin addition, however, dramatically influenced the kinetic properties of NADH dehydrogenase. It is proposed that in heart mitochondria, calcium does not affect directly the components of electron transport but it may influence the activity of NADH dehydrogenase indirectly by increasing delta psi.

Adenosine Diphosphate↗
PubMed1987

Evidence for succinate production by reduction of fumarate during hypoxia in isolated adult rat heart cells.

It has been demonstrated that perfusion of myocardium with glutamic acid or tricarboxylic acid cycle intermediates during hypoxia or ischemia, improves cardiac function, increases ATP levels, and stimulates succinate production. In this study isolated adult rat heart cells were used to investigate the mechanism of anaerobic succinate formation and examine beneficial effects attributed to ATP generated by this pathway. Myocytes incubated for 60 min under hypoxic conditions showed a slight loss of ATP from an initial value of 21 +/- 1 nmol/mg protein, a decline of CP from 42 to 17 nmol/mg protein and a fourfold increase in lactic acid production to 1.8 +/- 0.2 mumol/mg protein/h. These metabolite contents were not altered by the addition of malate and 2-oxoglutarate to the incubation medium nor were differences in cell viability observed; however, succinate release was substantially accelerated to 241 +/- 53 nmol/mg protein. Incubation of cells with [U-14C]malate or [2-U-14C]oxoglutarate indicates that succinate is formed directly from malate but not from 2-oxoglutarate. Moreover, anaerobic succinate formation was rotenone sensitive. We conclude that malate reduction to succinate occurs via the reverse action of succinate dehydrogenase in a coupled reaction where NADH is oxidized (and FAD reduced) and ADP is phosphorylated. Furthermore, by transaminating with aspartate to produce oxaloacetate, 2-oxoglutarate stimulates cytosolic malic dehydrogenase activity, whereby malate is formed and NADH is oxidized. In the form of malate, reducing equivalents and substrate are transported into the mitochondria where they are utilized for succinate synthesis.

Adenosine Triphosphate↗
PubMed2006

Succinate dehydrogenase functioning by a reverse redox loop mechanism and fumarate reductase in sulphate-reducing bacteria.

Sulphate- or sulphur-reducing bacteria with known or draft genome sequences (Desulfovibrio vulgaris, Desulfovibrio desulfuricans G20, Desulfobacterium autotrophicum [draft], Desulfotalea psychrophila and Geobacter sulfurreducens) all contain sdhCAB or frdCAB gene clusters encoding succinate : quinone oxidoreductases. frdD or sdhD genes are missing. The presence and function of succinate dehydrogenase versus fumarate reductase was studied. Desulfovibrio desulfuricans (strain Essex 6) grew by fumarate respiration or by fumarate disproportionation, and contained fumarate reductase activity. Desulfovibrio vulgaris lacked fumarate respiration and contained succinate dehydrogenase activity. Succinate oxidation by the menaquinone analogue 2,3-dimethyl-1,4-naphthoquinone depended on a proton potential, and the activity was lost after degradation of the proton potential. The membrane anchor SdhC contains four conserved His residues which are known as the ligands for two haem B residues. The properties are very similar to succinate dehydrogenase of the Gram-positive (menaquinone-containing) Bacillus subtilis, which uses a reverse redox loop mechanism in succinate : menaquinone reduction. It is concluded that succinate dehydrogenases from menaquinone-containing bacteria generally require a proton potential to drive the endergonic succinate oxidation. Sequence comparison shows that the SdhC subunit of this type lacks a Glu residue in transmembrane helix IV, which is part of the uncoupling E-pathway in most non-electrogenic FrdABC enzymes.

Amino Acid Sequence↗
PubMed1997

The effect of the bacterial product, succinic acid, on neutrophil bactericidal activity.

We investigated the effect of succinic acid on neutrophil bactericidal activity in a model of intra-abdominal abscess induced in mice by the peritoneal inoculation of 5 x 10(6) cfu ml-1 E. coli and 5 x 10(8) cfu ml-1 B. fragilis plus 1 mg of bran as faecal fibre analogue. The mean pH of the induced abscesses at week 1 was 6.7, higher than the pH associated with succinic acid inhibitory activity. We therefore determined the effect of succinic acid (0-100 mM) at pH 6.7 on the bactericidal activity of mouse bone marrow-derived neutrophils. Phagocytic killing of Proteus mirabilis by neutrophils was significantly inhibited by 30-100 mM succinic acid at pH 6.7 but there was no significant effect of succinic acid on engulfment of bacteria at this pH. However, significant inhibition of intracellular killing (assayed by adding succinic acid to suspensions of neutrophils which had engulfed bacteria in low serum concentrations but in the absence of succinic acid) was noted at 70 and 100 mM. These results indicate that succinic acid inhibits neutrophil bactericidal activity at a physiological pH, principally through inhibition of intracellular killing mechanisms and therefore contributing to bacterial persistence in this model of abscess formation.

Abdominal Abscess↗
PubMed1973

Succinate oxidase in Neurospora.

Two kinetically distinct states of succinate oxidase have been detected in the mitochondria of Neruospora crassa. One state has a K(m) for succinate of 4.1 x 10(-3)m, and the other has a K(m) for succinate of 3.5 x 10(-4)m. The high K(m) state was found in freshly extracted mitochondria from either 20- or 72-hr mycelium. However, the succinate oxidase activity in mitochondria from 20-hr mycelium rapidly deteriorated in vitro, leaving a stable residual activity with the lower K(m) for succinate. Adenosine triphosphate (ATP) plus Mg(2+) stabilized the high K(m) state in these preparations. The high K(m) state of succinate oxidase was further characterized by a two- to threefold increase in activity over the pH range 6.6 to 8.0 and by classical competitive inhibition by fumarate and malonate. By contrast, the low K(m) state of succinate oxidase showed a relatively flat response to pH over the range 6.6 to 8.0 and a nonclassical pattern of inhibition by fumarate and malonate, as shown by nonlinear plots of reciprocal velocity versus reciprocal substrate concentration in the presence of inhibitor or reciprocal velocity versus inhibitor concentration at fixed substrate concentrations. The relationship of mycelial age to the in vitro stability of succinate oxidase is considered with reference to probable changes in the relative pool sizes of extra- and intramitochondrial ATP in response to changes in the rate of glycolysis.

Adenosine Triphosphate↗
PubMed1976

Hypoxia: a succinate-fumerate electron shuttle between peripheral cells and lung.

The objective of this investigation was to determine if the succinate that accumulates in anoxic or hypoxic tissues of mammals is (a) increased in concentration in the blood, (b) excreted in the urine or (c) recycled in some manner. Rats were subjected to 0.4 atm and the plasma analyzed for succinate and fumarate at 2 hours, 24 hours and 28 days. Significant increases of succinate or succinate plus fumarate were obtained at 2 hours and 28 days at 0.4 atm. Analysis of 24-hour samples of urine obtained from controls and animals at 0.4 atm for 28 days demonstrated that no substantial increase in succinate excretion occurred with acclimation. Lung slices were incubated in Krebs-Ringer bicarbonate and succinate and gassed with O2:CO2 (95:5). Such oxygenated lung slices not only utilized succinate but produced a comparable quantity of fumerate plus malate. It is concluded that succinate produced from fumarate and alpha-ketoglutarate in peripheral hypotic tissue is transported by the blood to the oxygenated lungs. There it is oxidized to fumarate and recycled as fumarate and malate to the periphery. In this way metabolites can act as electron shuttles between peripheral cells and lung.

Animals↗
PubMed2001

Importance of redox balance on the production of succinic acid by metabolically engineered Escherichia coli.

We had previously shown that succinic acid production in a pfl ldhA double mutant strain of Escherichia coli could be enhanced by amplifying the malic enzyme activity. However, recombinant E. coli NZN111 (F- Apfl::Cam ldhA::Kan) harboring pTrcML, a plasmid containing the E. coli malic enzyme gene, produced a considerable amount of malic acid along with the desired product, succinic acid. To have an insight into the intracellular metabolism, metabolic control analysis was carried out. From the results of a simulation, it was predicted that supplying additional reducing power could enhance succinic acid production. More reduced carbon substrate sorbitol was thus examined for the possibility of matching the potential during succinic acid production. When NZN111 (pTrcML) was cultured in LB medium containing 20 g sorbitol/l under a CO2 atmosphere, 10 g succinic acid/l was produced. The apparent yield of succinic acid was 1.1 g succinic acid/g sorbitol, which is 85% of the maximum theoretical yield. Therefore, it was found that redox balancing was important for the enhanced production of succinic acid in metabolically engineered E. coli.

Carbon Dioxide↗
PubMed2005

Effect of carbon sources differing in oxidation state and transport route on succinate production in metabolically engineered Escherichia coli.

In mixed-acid fermentation, succinate synthesis requires one mole of phosphoenolpyruvate (PEP), one mole of CO2, and two moles of NADH for every mole of succinate to be formed. Different carbon sources with different properties were used to address these requirements. Sorbitol generates one more mole of NADH than glucose. Fermentation of sorbitol was shown in this study (and by others) to produce significantly more succinate than fermentation of glucose, due to increased NADH availability. Xylose fermentation conserves the intracellular PEP pool, since its transport does not require the phosphotransferase system normally used for glucose transport. The extra PEP can then be assimilated in the succinate pathway to improve production. In this study, fermentation of xylose did yield higher succinate production than glucose fermentation. Subsequent inactivation of the acetate and lactate pathways was performed to study metabolite redistribution and the effect on succinate production. With the acetate pathway inactivated, significant carbon flux shifted toward lactate rather than succinate. When both acetate and lactate pathways were inactivated, succinate yield ultimately increased with a concomitant increase in ethanol yield.

Acetates↗
PubMed1983

Association between the alpha-ketoglutarate dehydrogenase complex and succinate thiokinase.

The kinetic parameters of the individual reaction of pig heart alpha-ketoglutarate dehydrogenase complex, succinate thiokinase and the alpha-ketoglutarate dehydrogenase complex-succinate thiokinase coupled system were studied. The KCoAm of alpha-ketoglutarate dehydrogenase complex and the K-succinyl CoAm of succinate thiokinase decreased in the coupled system when compared to those of the individual enzyme reactions. This phenomenon can be explained by the interaction between the alpha-ketoglutarate dehydrogenase complex and succinate thiokinase. By means of poly(ethylene glycol) precipitation, ultracentrifugation and gel chromatography we were able to detect a physical interaction between the alpha-ketoglutarate dehydrogenase complex and succinate thiokinase. Of the seven investigated proteins only succinate thiokinase showed association with alpha-ketoglutarate dehydrogenase complex. On the other hand, succinate thiokinase did not associate with other high molecular weight mitochondrial enzymes such as pyruvate dehydrogenase complex and glutamate dehydrogenase. On this basis, the interaction between succinate thiokinase and alpha-ketoglutarate dehydrogenase complex was assumed to be specific. These in vitro data raise the possibility that a portion of the citric acid cycle enzymes exists as a large multienzyme complex in the mitochondrial matrix.

Animals↗
PubMed2000

The distal heme center in Bacillus subtilis succinate:quinone reductase is crucial for electron transfer to menaquinone.

Succinate:quinone reductases are membrane-bound enzymes that catalyze electron transfer from succinate to quinone. Some enzymes in vivo reduce ubiquinone (exergonic reaction) whereas others reduce menaquinone (endergonic reaction). The succinate:menaquinone reductases all contain two heme groups in the membrane anchor of the enzyme: a proximal heme (heme b(P)) located close to the negative side of the membrane and a distal heme (heme b(D)) located close to the positive side of the membrane. Heme b(D) is a distinctive feature of the succinate:menaquinone reductases, but the role of this heme in electron transfer to quinone has not previously been analyzed. His28 and His113 are the axial ligands to heme b(D) in Bacillus subtilis succinate:menaquinone reductase. We have individually replaced these His residues with Leu and Met, respectively, resulting in assembled membrane-bound enzymes. The H28L mutant enzyme lacks succinate:quinone reductase activity probably due to a defective quinone binding site. The H113M mutant enzyme contains heme b(D) with raised midpoint potential and is impaired in electron transfer to menaquinone. Our combined experimental data show that the heme b(D) center, into which we include a quinone binding site, is crucial for succinate:menaquinone reductase activity. The results support a model in which menaquinone is reduced on the positive side of the membrane and the transmembrane electrochemical potential provides driving force for electron transfer from succinate via heme b(P) and heme b(D) to menaquinone.

Bacillus subtilis↗
PubMed2005

Intramolecular hydrogen bonding in disubstituted ethanes. A comparison of NH...O- and OH...O- Hydrogen bonding through conformational analysis of 4-amino-4-oxobutanoate (succinamate) and monohydrogen 1,4-butanoate (monohydrogen succinate) anions.

Relative strengths of amide NH...O- and carboxyl OH...O- hydrogen bonds were investigated via conformational analysis of succinamate and monohydrogen succinate anions with the aid of vicinal proton-proton NMR couplings and B3LYP DFT quantum mechanical calculations for a variety of solvents. New experimental results for succinamate are compared with those obtained from previous studies of monohydrogen succinate. While some computational results for monohydrogen succinate were published previously, the results contained herein are the product of a more powerful methodology than that used earlier. The experimental results clearly show that intramolecular hydrogen-bond formation is more favored in aprotic solvents than in protic solvents for both molecules. Furthermore, the preference of the succinate monoanion for the gauche conformation is much stronger in aprotic solvents than that of succinamate, indicating that the OH...O- hydrogen bond is substantially stronger than its NH...O- counterpart, despite the approximately 5 kcal cost for formation of the E configuration of the carboxyl group needed to make an intramolecular hydrogen bond. The actual energy differences between formation of internal hydrogen bonds for monohydrogen succinate and succinamate anion were estimated by comparison of the relative values of K1 of the respective acids in water and DMSO by a procedure first developed by Westheimer. Recent theoretical work with succinamate highlights the necessity of considering substituent orientational degrees of freedom to understand the conformational equilibria of the central CH2-CH2 torsions in disubstituted ethanes. Similar methodology is applied here to succinic acid monoanion, by mapping potential-energy surfaces with respect to the CH2-CH2 torsional, carboxyl-substituent rotational, and carboxyl-proton E/Z isomeric degrees of freedom. Boltzmann populations were compared with gauche populations estimated from the experimentally determined coupling constants. The quantum mechanical results for succinamate show a much weaker tendency toward hydrogen bonding than for the succinic acid monoanion. However, the theoretical methods employed appear to substantially overestimate contributions from intramolecularly hydrogen-bonded structures for the succinic acid monoanion when compared with experimental results. Natural bond orbital analysis, applied to the quantum mechanical wave functions of fully optimized gauche and trans structures, showed a strong correlation between the population of amide sigma*(N-H) and carboxyl sigma*(O-H) antibonding orbitals and apparent hydrogen-bonding behavior.

Anions↗
PubMed1981

Possible occurrence and role of an essential histidyl residue in succinate dehydrogenase.

Diethylpyrocarbonate (Et2PC) inhibits the succinate dehydrogenase [succinate:(acceptor) oxidoreductase, EC 1.3.99.1] activity of submitochondrial particles, Complex II (succinate:ubiquinone oxidoreductase), and the soluble, pure succinate dehydrogenase. The reaction order with respect to Et2PC concentration is close to unity, suggesting modification of one essential residue per active unit of the enzyme. The pH profile of Et2PC inhibition, the partial reversal of inhibition by hydroxylamine, and the spectral change of the Et2PC-treated enzyme in the UV region suggest modification of a histidyl residue. Succinate dehydrogenase activity can be protected against Et2PC inhibition by succinate, fumarate, malonate, or oxaloacetate (also by activating anions such as ClO4(-) and Br-), suggesting that the Et2PC-modified essential residue might be at the active site. In both submitochondrial particles and the purified enzyme, succinate dehydrogenase activity is highest and relatively constant at pH greater than or equal to 7.0 and diminishes precipitously at pH less than 7.0. By contrast, fumarate reductase activity is highest at pH less than or equal to 7.0 and diminishes at pH greater than 7.0. These results are consistent with the possible participation of the unprotonated and protonated forms of the imidazole moiety of the putative histidyl residue, respectively, in succinate oxidation and fumarate reduction.

Animals↗
PubMed1979

Ca2+-induced activation of succinate dehydrogenase and the regulation of mitochondrial oxidative reactions.

1. In rat liver mitochondria in vitro, an activation of succinate dehydrogenase [succinate: (2,6-dichloroindophenol)oxido-reductase], an inner membrane enzyme, was induced by Ca2+ at extramitochondrial concentrations (about 1.3 micron) close to those estimated in the cytosol. 2. The activation required both substrate (succinate) and ATP, and occurred whether mitochondria were coupled (Ca2+ could be accumulated) or uncoupled (Ca2+ could not be accumulated) by classical uncouplers. 3. The activation by Ca2+ of the uncoupled mitochondria was accompanied by a modest but significant change in the mitochondrial morphology as judged from light scattering measurements and electron microscopy. 4. In the uncoupled mitochondria, oxaloacetate added externally diminished the activation by Ca2+. In addition, the amount of oxaloacetate produced endogenously from succinate via malate fell after Ca2+ and ATP addition. However, the extent of the fall in mitochondrial oxaloacetate did not correlate with the degree of activation of succinate dehydrogenase. 5. The activation by Ca2+ of the uncoupled mitochondria was accompanied by a reductive shift of pyridine nucleotide and coenzyme Q, and an oxidative shift of flavoproteins and cytochromes b, c, and a-a3. 6. In the situation where the Ca2+-induced activation of succinate dehydrogenase (and consequently succinate oxidation) took place in the uncoupled mitochondria, oxidations of 3-hydroxybutyrate and pyruvate were markedly suppressed. 7. From the above findings, it is concluded that Ca2+ action on the mitochondrial inner membrane activates mitochondrial succinate dehydrogenase, and this action produces an inhibition of electron transport between NAD and flavoprotein. In view of the location of these reactions in the inner membrane, a conformation change of the membrane is suggested as a common cause.

Animals↗
PubMed1972

Hyperbaric oxygen exposures at 3 and 4 atmospheres absolute pressure for experimental gas gangrene: succinate protection against oxygen toxicity.

The concurrent effect of succinate administration to protect against oxygen toxicity and of hyperbaric oxygen (HBO) exposures to treat model gas gangrene in mice was tested to determine whether succinate would interfere with the therapeutic efficacy of HBO. HBO (seven 90-min exposures) at 3 atmospheres absolute pressure (ATA) had been shown to reduce significantly the mortality of mice injected with Clostridium perfringens suspended in 10 mug of Adrenalin. When succinate was tested with this system, mortality of HBO-exposed infected animals was again significantly reduced (79% control mortality versus 17% HBO-exposed mortality), indicating that succinate does not interfere with the action of HBO. Exposures to 4 ATA of O(2) were evaluated in the same model clostridial infection with succinate used to prevent oxygen toxicity. Five 30-min exposures at 4 ATA reduced the mortality of infected animals (62% control versus 6% HBO-exposed mortality). Intraperitoneal succinate injections (10 mmoles/kg) were given 20 to 25 min prior to four of the seven 3-ATA exposures and before three of the five 4-ATA exposures. The intermittent succinate injections gave significant protection against the development of oxygen toxicity in infected and noninfected mice at both O(2) pressures. These studies support the potential clinical use of succinate or other oxygen-protective agents (i) to shorten HBO exposure times by using higher pressures to deliver the necessary O(2) dose, (ii) to increase the O(2) dose for difficult clinical situations by using maximal exposures at 4 ATA or more prolonged exposures at 2 to 3 ATA, and (iii) to continue HBO exposures in patients who require treatment but develop symptoms of oxygen toxicity.

Animals↗
PubMed1970

Biosynthesis of alpha-ketoglutarate by the reductive carboxylation of succinate in Bacteroides ruminicola.

Experiments with growing cells and with cell-free extracts of Bacteroides ruminicola indicate that this anaerobic bacterium can synthesize alpha-ketoglutarate by a reductive carboxylation of succinate. When the organism was grown in medium containing succinate-1,4-(14)C, most of the radioactivity in cells was in the protein fraction and most of the (14)C in protein was in the glutamic acid family of amino acids (glutamate, proline, and arginine). When unlabeled succinate was added to culture medium containing glucose-U-(14)C, incorporation of radioactivity into the glutamic acid family of amino acids was greatly reduced. This supports the concept that succinate is an intermediate in synthesis of alpha-ketoglutarate. Cell-free extracts of the organism incubated with succinate-1,4-(14)C incorporated (14)C into amino acids and most of this was found in glutamate. The cofactors which stimulate glutamate synthesis from succinate by extracts from these cells appear to be similar to the factors that have been demonstrated with extracts from photosynthetic bacteria. The position of label in glutamate synthesized from succinate-1,4-(14)C, the probable absence of isocitric dehydrogenase, and studies with labeled citrate and with inhibitors of citric acid cycle enzymes support the concept of a reductive carboxylation of succinate as the only, or at least a major, mechanism for synthesis of alpha-ketoglutarate in this organism. This appears to be the first evidence for a net synthesis of alpha-ketoglutarate by this reaction in a nonphotosynthetic heterotrophic organism.

Bacteroides↗
PubMed1972

Requirement of succinate for the growth of Vibrio succinogenes.

Vibrio succinogenes required relatively small amounts of succinate for growth when formate plus nitrate was supplied as the energy source. The requirement for succinate was not apparent when formate plus fumarate was the energy source because fumarate is reduced to succinate. l-Asparagine, fumarate, and malate replaced succinate, and it appears likely that they do so by being converted to succinate. Formate plus l-aspartate or l-asparagine served as energy sources for growth. The stoichiometry of the reduction of aspartate with H(2) by resting cells suggests an aspartase reaction followed by reduction of fumarate to succinate. Oxalacetate or pyruvate plus bicarbonate did not substitute for succinate, nor did many other compounds that were tested. (14)C-succinate was mainly incorporated into the alcohol-soluble fraction of cells, although there was significant incorporation into the hot trichloroacetic acid-soluble and -insoluble fractions.

Asparagine↗
PubMed2000

Succinate:quinol oxidoreductases in the cyanobacterium synechocystis sp. strain PCC 6803: presence and function in metabolism and electron transport.

The open reading frames sll1625 and sll0823, which have significant sequence similarity to genes coding for the FeS subunits of succinate dehydrogenase and fumarate reductase, were deleted singly and in combination in the cyanobacterium Synechocystis sp. strain PCC 6803. When the organic acid content in the Deltasll1625 and Deltasll0823 strains was analyzed, a 100-fold decrease in succinate and fumarate concentrations was observed relative to the wild type. A similar analysis for the Deltasll1625 Deltasll0823 strain revealed that 17% of the wild-type succinate levels remained, while only 1 to 2% of the wild-type fumarate levels were present. Addition of 2-oxoglutarate to the growth media of the double mutant strain prior to analysis of organic acids in cells caused succinate to accumulate. This indicates that succinate dehydrogenase activity had been blocked by the deletions and that 2-oxoglutarate can be converted to succinate in vivo in this organism, even though a traditional 2-oxoglutarate dehydrogenase is lacking. In addition, reduction of the thylakoid plastoquinone pool in darkness in the presence of KCN was up to fivefold slower in the mutants than in the wild type. Moreover, in vitro succinate dehydrogenase activity observed in wild-type membranes is absent from those isolated from the double mutant and reduced in those from the single mutants, further indicating that the sll1625 and sll0823 open reading frames encode subunits of succinate dehydrogenase complexes that are active in the thylakoid membrane of the cyanobacterium.

Chlorophyll↗
PubMed1991

Sodium-dependent succinate transport by isolated chick intestinal cells.

Isolated chick intestinal epithelial cells take up succinate by a Na(+)-coupled transport system similar in some characteristics to those described for renal epithelium. The transport system exhibits a hyperbolic dependence on succinate concentration but a sigmoidal dependence on Na+ concentration. Best nonlinear fit of the Na+ dependence data to the Hill equation indicates a Michaelis constant for half-maximal transport rate (Km) for Na+ of approximately 20 mM, a maximal transport rate (Vmax) of 1.1 nmol succinate.min-1.mg protein-1, and a Hill coefficient of 2.5. Nearly equivalent fit was obtained with trial Hill coefficients down to 2.0. The data for succinate dependence indicated a Km of 25 microM and Vmax of 1.05 nmol.min-1.mg protein-1. The kinetic parameters indicate a higher affinity, lower capacity system than for succinate transport in the renal brush-border system. Thiocyanate-induced diffusion potentials cause no change in Na(+)-dependent succinate influx despite pronounced effects on the influx of tetraphenylphosphonium and on Na(+)-dependent alpha-methylglucoside (AMG) and alanine uptake. Several other dicarboxylic and tricarboxylic metabolic intermediates (but not the dicarboxylic amino acids) compete with succinate for uptake via the transport system. The data are consistent with the likelihood that these cells have a succinate transport system with a 2Na+:1succinate stoichiometry per transport cycle. The system catalyzes no net charge transfer and is therefore different from the potential-responsive succinate transporter described for renal tissue.

Alanine↗