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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two techniques have been applied to the determination of the number and type (2-Fe, 4-Fe) of iron-sulfur centers in the iron-sulfur flavoprotein succinate dehydrogenase [succinate:(acceptor) oxidoreductase, EC 1.3.99.1]. One procedure uses p-CF3C6H4SH as an extrusion reagent and Fourier transform 19F nuclear magentic resonance as the method of detection and quantitation of extruded cores of these centers in the form of [Fe2S2(SRF)4]2- and [Fe4S4(SRF)4]2- (RF = p-C6H4CF3). The second procedure, interprotein core transfer, involves thiol displacement of iron-sulfur cores followed by specific core transfer to the apoproteins of Bacillus polymyxa ferredoxin and adrenodoxin. Detection and quantitation are accomplished by electron paramagnetic resonance of reduced proteins at low temperatures. Both procedures clearly show that succinate dehydrogenase contains two dimeric (Fe2S2) and one tetrameric (Fe4S4) centers per mole of histidyl flavin, accounting for all eight nonheme iron and eight labile sulfur atoms found by chemical analysis. These results remove uncertainties created by the less than stoichiometric amounts of binuclear centers detected by electron paramagnetic resonance after dithionite reduction and provide secure characterization of the iron-sulfur centers in this enzyme.
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PMID:Characterization of the iron-sulfur centers in succinate dehydrogenase. 22 82

When anaerobic cultures of Propionibacterium pentosaceum were shifted to low dissolved-oxygen concentration (D.O.C.), acetate production from lactate diminished and propionate production stopped, whereas pyruvate accumulated and oxygen was consumed. Assuming that energy is generated in the electron transfer to oxygen, YATP values (g dry wt bacteria/mole ATP) of between 7.2 and 11.9 were calculated from molar growth yields and product formation. When oxidative phosphorylation in the electron transfer to oxygen was ignored, unreasonably high YATP values were obtained. From these results it is concluded that energy is indeed generated in the electron transfer to oxygen. However, synthesis of cytochrome b was strongly repressed by oxygen. Furthermore, synthesis of all catabolic enzymes studied was impaired in bacteria growing at low D.O.C. Thus, the anaerobic character of P. pentosaceum may be explained by the inhibition of synthesis of both cytochrome b and enzymes in the presence of oxygen. It was demonstrated that nitrate reductase is synthesized constitutively in P. pentosaceum. Synthesis of nitrate reductase was stimulated by nitrate and repressed by oxygen. Synthesis of fumarate reductase was also repressed by oxygen, whereas only a small effect of nitrate on this enzyme was observed. However, propionate formation is inhibited during growth with nitrate. The absence of propionate formation in the presence of oxygen and nitrate is explained by inavailability of NADH needed for the conversion of oxaloacetate into malate in the reductive pathway to succinate, so that succinate and propionate cannot be formed.
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PMID:Lactate metabolism in Propionibacterium pentosaceum growing with nitrate or oxygen as hydrogen acceptor. 108 38

The membrane-bound succinate dehydrogenase (SDH; EC 1.3.99.1) of Bacillus pumilus strain 5 was investigated as succinate:ferricyanide oxidoreductase activity at 27 degrees C. A Km of 8.3 x 10(-3) M was obtained, and the Vmax was 1.8 x 10(-6) mole succinate dehydrogenated min-1 mg-1 membrane protein, at a substrate (succinate) concentration below 40 x 10(-3) M. Above this succinate concentration the Km was 102 x 10(-3) M and the Vmax was 3.7 x 10(-6) mole succinate min-1 mg-1 membrane protein. Para-benzoquinone or 2,4-dinitrophenylhydrazine, in micromolar amounts inhibited the enzyme by serving as an electron sink. Hydroxyl radical (OH.) scavengers, mannitol and benzoate, activated the enzyme, while superoxide dismutase (SOD) had no effect on the enzyme. Thus, the mechanism of electron transfer from succinate to Fe(CN)3-(6) through SDH does not involve superoxide (O2-) as a rate-limiting intermediate.
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PMID:Membrane-bound succinate dehydrogenase of Bacillus pumilus strain 5: effects of modulators of monoelectron transfer. 251 38

Based on the presence and absence of enzyme activities, the biochemical pathways for the fermentation of inulin by Clostridium thermosuccinogenes DSM 5809 are proposed. Activities of nine enzymes (lactate dehydrogenase, phosphoenolpyruvate carboxylase, malate dehydrogenase, fumarase, fumarate reductase, phosphotransacetylase, acetate kinase, pyruvate kinase, and alcohol dehydrogenase) were measured at four temperatures (37, 47, 58, and 70 degrees C). Each of the enzymes increased 1.5 to 2.0-fold in activity between 37 and 58 degrees C, but only lactate dehydrogenase, fumarate reductase, malate dehydrogenase, and fumarase increased at a similar rate between 58 and 70 degrees C. No acetate kinase activity was observed at 70 degrees C. Arrhenius energies were calculated for each of these nine enzymes and were in the range of 9.8 to 25.6 kcal/mol. To determine if a relationship existed between product formation and enzyme activity, serum bottle fermentations were completed at the four temperatures. Maximum yields (in moles per mole hexose unit) for succinate (0.23) and acetate (0.79) and for biomass (29.5 g/mol hexose unit) occurred at 58 degrees C, whereas the maximum yields for lactate (0.19) and hydrogen (0.25) and the lowest yields for acetate (0.03) and biomass (19.2 g/mol hexose unit) were observed at 70 degrees C. The ratio of oxidized products to reduced products changed significantly, from 0.52 to 0.65, with an increase in temperature from 58 to 70 degrees C, and there was an unexplained detection of increased reduced products (ethanol, lactate, and hydrogen) with a concomitant decrease in oxidized-product formation at the higher temperature.
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PMID:Elucidation of enzymes in fermentation pathways used by Clostridium thermosuccinogenes growing on inulin. 1061 31

Derivatives of Escherichia coli C were engineered to produce primarily succinate or malate in mineral salts media using simple fermentations (anaerobic stirred batch with pH control) without the addition of plasmids or foreign genes. This was done by a combination of gene deletions (genetic engineering) and metabolic evolution with over 2,000 generations of growth-based selection. After deletion of the central anaerobic fermentation genes (ldhA, adhE, ackA), the pathway for malate and succinate production remained as the primary route for the regeneration of NAD+. Under anaerobic conditions, ATP production for growth was obligately coupled to malate dehydrogenase and fumarate reductase by the requirement for NADH oxidation. Selecting strains for improved growth co-selected increased production of these dicarboxylic acids. Additional deletions were introduced as further improvements (focA, pflB, poxB, mgsA). The best succinate biocatalysts, strains KJ060(ldhA, adhE, ackA, focA, pflB) and KJ073(ldhA, adhE, ackA, focA, pflB, mgsA, poxB), produce 622-733 mM of succinate with molar yields of 1.2-1.6 per mole of metabolized glucose. The best malate biocatalyst, strain KJ071(ldhA, adhE, ackA, focA, pflB, mgsA), produced 516 mM malate with molar yields of 1.4 per mole of glucose metabolized.
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PMID:Combining metabolic engineering and metabolic evolution to develop nonrecombinant strains of Escherichia coli C that produce succinate and malate. 1797 30

Mole rats of the Spalax ehrenbergi superspecies are blind subterranean rodents that live under fluctuating oxygen supply, reduced to a measured 6% O(2), and mostly probably lower, during the rainy season. Fiber typing of muscles of the neck (trapezius) and leg (gastrocnemius, quadriceps) using standard histochemical techniques (succinic dehydrogenase, myosin ATPase) showed that the muscle fibers of mole rats in natural settings, as well as after extended captivity, were predominantly type IIa. The same muscles in laboratory rats showed the full range of fiber types. In contrast, the hearts of the mole rats and the laboratory rats were very similar. Our results indicate that skeletal muscle in the mole rats appears to have evolved in response to specific environmental demands to permit intensive endurance burrowing activities under conditions of severe or chronic hypoxia.
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PMID:Adaptive features of skeletal muscles of mole rats (Spalax ehrenbergi) to intensive activity under subterranean hypoxic conditions. 1867 7