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At least 19 recordsLinked to original sources
PubMed1978

Succinate dehydrogenase-dependent nutritional requirement for succinate in mutants of Escherichia coli K12.

Lipoic acid (lip) and 2-oxoglutarate dehydrogenase (sucA) mutants of Escherichia coli K12 exhibit a requirement for exogenous succinate during aerobic growth on glucose minimal medium. Reversion studies have shown that this requirement can be suppressed by gal-linked mutations which inactivate succinate dehydrogenase. Biochemical and genetic studies confirmed that the succinate dehydrogenase gene (sdh) is affected and that suppression is mediated by the same intergenic and indirect mechanism that generates succinate independence in partial revertants of lipoamide dehydrogenase mutants (Creaghan & Guest, 1977). A series of isogenic strains containing all combinations of mutations affecting 2-oxoglutarate dehydrogenase (sucA), succinate dehydrogenase (sdh), isocitrate lyase (aceA) and fumarate reductase (frd) in a background lacking succinate semialdehyde dehydrogenase, was constructed to assess the importance of these enzymes as sources of endogenous succinate (succinyl-CoA) during aerobic and anaerobic growth on glucose. Only strains combining a deficiency in 2-oxoglutarate dehydrogenase with the presence of an active succinate dehydrogenase required succinate for aerobic growth. In all mutants, including the triple mutant (frd sucA aceA), the succinate requirement was suppressed by inactivating succinate dehydrogenase. The aerobic growth rates of succinate-independent strains were most affected by lack of isocitrate lyase but only two mutants (sdh sucA aceA and frd sdh sucA aceA) grew faster with added succinate: the growth yields were lowered by deficiencies in isocitrate lyase and also succinate dehydrogenase. It is concluded that very little succinate is needed for biosynthesis during aerobic growth on glucose and the requirement for relatively high concentrations of succinate (2 mM) by mutants lacking 2-oxoglutarate dehydrogenase or related functions stems from the presence of active succinate dehydrogenase. Anaerobically, either isocitrate lyase or fumarate reductase is essential for succinate-independent growth on glucose.

Acetates↗
PubMed1979

Studies on the succinate dehydrogenating system. I. Kinetics of the succinate dehydrogenase interaction with a semiquindiimine radical of N,N,N',N'-tetramethyl-p-phenylenediamine.

1. The activities of the soluble reconstitutively active succinate dehydrogenase (EC 1.3.99.1) measured with three artificial electron acceptors, e.g. ferricyanide, phenazine methosulfate and free radical of N,N,N',N'-tetramethyl-p-phenylenediamine (WB), have been compared. The values estimated by extrapolation to infinite acceptor concentration using double reciprocal plots 1/v versus 1/[acceptor] are nearly the same for ferricyanide and phenazine methosulfate and about twice as high for the WB. 2. The double reciprocal plots 1/v versus 1/[succinate] in the presence of malonate at various concentrations of WB give a series of straight lines intercepting in the third quadrant. The data support the mechanism of the overall reaction, in which the reduced enzyme is oxidized by WB before dissociation of the enzyme-product complex. 3. The dependence of the rate of the overall reaction on WB concentration shows that only one kinetically significant redox site of the soluble succinate dehydrogenase is involved in the reduction of WB. 4. Studies of the change of V and Km values during aerobic inactivation of the soluble enzyme suggest that only 'the low Km ferricyanide reactive site' (Vinogradov, A.D., Gavrikova, E.V. and Goloveshkina, V.G. (1975) Biochem. Biophys, Res. Commun. 65, 1264--1269) is involved in reoxidation of the reduced enzyme by WB. 5. The pH dependence of V for the succinate-WB reductase reaction shows that the group of the enzyme with the pKa value of 6.7 at 22 degrees C is responsible for the reduction of dehydrogenase in the enzyme-substrate complex. 6. When WB interacts with the succinate-ubiquinone region of the respiratory chain, the double reciprocal plot 1/v versus 1/[WB] gives a straight line. The thenoyltrifluoroacetone inhibition of succinate-ubiquinone reductase or extraction of ubiquinone alter the 1/v versus 1/[WB] plots for the curves with a positive initial slope intercepting the ordinate at the same V as in the native particles. The data support the mechanism of succinate-ubiquinone reduction, in which no positive modulation of succinate dehydrogenase by ubiquinone exist in the membrane.

Aerobiosis↗
PubMed1975

The steady state activity of succinate dehydrogenase in the presence of opposing effectors.II. Reductive activation of succinate dehydrogenase in presence of oxaloacetate.

The extent of the deactivation of the mitochondrial succinate dehydrogenase by oxaloacetate is a function of the redox state of the enzyme. Oxidized enzyme is deactivated by much lower concentrations of oxaloacetate than those needed to deactivate reduced enzyme. An accurate method for measuring this relationship is the redox titration of the enzymic activity of succinate dehydrogenase, carried out in the presence of oxaloacetate. For each concentration of oxaloacetate a different redox titration curve was reported with the apparent mid-potential decreasing with increasing oxaloacetate. These results are compatible with a model which proposes that both oxidized and reduced enzymes can form the catalytically non-active complex with oxaloacetate, but that the complex formed the the oxidized enzyme is more stable than that formed by the reduced enzyme. When the oxaloacetate concentration is low, reduction of the enzyme will lower the fraction of the succinate dehydrogenase-oxaloacetate complex, a reaction which we observe as reductive activation of the enzyme. If this experiment is repeated in the presence of high concentration of oxaloacetate, no activation of the enzyme takes place, but the low stability of the reduced enzyme oxaloacetate complex is revealed by the rapid exchange of the enzyme-bound oxaloacetate with the free ligand. The rate of this exchange is extremely slow at high positive potential and becomes faster upon lowering of the poise potential. The reductive activation of the succinate dehydrogenase is regarded as a two step reaction. In the first step the reduced non-active complex releases the oxaloacetate and in the second step the active form of the enzyme is evolved. These two steps can be observed experimentally; Reductive activation at a redox potential higher than the mid-potential of the oxaloacetate-malate couple (minus 166 mV) is characterized by Ea = 18 Kca/mole, the final equilibrium level of activation decreases upon lowering of the temperature. Reduction activation of the enzyme at minus 240 mV is a very rapid reaction which goes to completion at all temperatures tested and has an activation energy of 12.5 Kcal/mole. The mechanism of the reductive activation and its possible role in the regulation of succinate dehydrogenase in the mitochondria is discussed.

Enzyme Activation↗
PubMed1977

Proton magnetic relaxation of aspartate transcarbamylase - succinate complexes.

Nuclear magnetic relaxation methods were used to investigate the interaction of the inhibitor succinate with aspartate transcarbamylase from Escherichia coli. Over the pH range 7 to 9, the dissociation constant for succinate remains less than the inhibitor concentration used for most of this work (0.05 M). As a result, the enzyme predominantly exists in a single "gross" conformational state. Succinate binding to this enzyme state (generally known as the R form) parallels the behavior seen previously with the isolated catalytic subunit (Beard, C. B., and Schmidt, P.G. (1973) Biochemistry 12, 2255-2264). The pH and temperature dependence of succinate proton relaxation rates, 1/T2 - 1/T1, in the presence of carbamyl phosphate, is interpreted in terms of a binding mechanism involving three forms of the enzyme, differing by their states of protonation. The least protonated form of the enzyme does not interact with succinate, the singly protonated species binds succinate to form a rapidly dissociating complex, and the doubly protonated species undergoes a conformational isomerization upon succinate binding, yielding a slow exchange complex. Relaxation data provide sufficient information to determine pKa values of 7.2 and 8.9 for two ionizing groups, as well as the dissociation constant for succinate in the fast exchange complex, Kd =1.6 X 10(-2) M. Rate constants for the forward and reverse steps of the isomerization, 1.3 X 10(3) s-1 and 33 s-1, respectively, indicate a significantly slower reverse rate from that obtained in the earlier NMR study of the isolated catalytic subunit. In experiments where the succinate concentration was varied, the relaxation rates showed sigmoidal binding of that ligand to the fast exchange complex above pH 9.1, (a) indicating cooperative binding of succinate, and (b) suggesting that above pH 9.1, the system cannot be characterized by a single dissociation constant, ionization constant, or relaxation effect. CTP and ATP were tested for their ability to affect succinate binding to the fast exchange complex. Heterotropic interactions were observed for CTP but not for ATP. Addition of low concentrations of the transition state analog N-(phosphonacetyl)-L-aspartate to the enzyme-carbamyl phosphate-succinate complex sharply decreased the relaxation rate, indicating that the measurements are sensitive only to succinate bound specifically to the active site.

Adenosine Triphosphate↗
PubMed1976

Uptake and efflux of succinic acid by uninduced mycelium of Claviceps purpurea.

Claviceps purpurea PRL 1980 grew on partially dissociated succinic acid (pH 4) but not on fully dissociated succinic acid (pH 7.2). Myeclium suspended in 42 mM solution of partially ionized succinic acid (pH 4; 60.1% nonionized, 39% monoanion, and 0.9% dianion, K+ salt) over a period of 25 min accumulated more succinic acid carbon than mycelium suspended in highly ionized solution (pH 6.8; 0.01% nonionized, 4.8% monoanion, and 95% dianion). The greater accumulation from partially ionized solution was not attributable solely to metabolism of succinic acid nor to the lower external concentration of potassium ion. Rate of uptake by sodium azide and iodoacetate-treated mycelium was proportional to external concentration at least up to 200 mumol/ml. External potassium or sodium ion was not required for uptake by inhibited or uninhibited mycelium and external sodium ion and glucose did not allow concentration of succinic acid. The internal concentrations of succinic acid carbon expressed as succinic acid in cell water were about the same as the external concentrations. Uptake was not appreciably affected by extent of ionization of external succinic acid but accumulation was markedly affected. A plot of accumulated succinic acid carbon against external pH produced a bimodal curve with the two maxima corresponding to the maximal concentrations of nonionized and monoanion succinic acid. The bimodal curve probably results from overlapping of two separate curves; the nonionized form accumulating efficiently because of one interaction with the cell and the monoanion form accumulating efficiently because of another interaction. Uptake from concentrated solution is by diffusion and efflux is rapid but not complete. Efflux is not retarded by presence of phosphate in the external solution.

Azides↗
PubMed1975

Succinate uptake and related proton movements in Escherichia coli K12.

1. The apparent Km values for succinate uptake by whole cells of Escherichia coli K12 depend on pH in the range 6.5-7.4.2. Uptake of succinate in lightly buffered medium is accompanied by proton uptake. 3. The apparent Km values for succinate uptake and for succinate-induced proton uptake are similar. 4. Approximately two protons enter the cell with each succinate molecule. 5. The pattern of inhibition of succinate uptake is similar to that of succinate-induced proton uptake. 6. Uptake of fumarate and malate, which share the succinate-transport system, is also accompanied by the uptake of approximately two protons per molecule of fumarate or malate. 7. Uptake of aspartate by the dicarboxylic acid-transport system is accompanied by the uptake of approximatley two protons per molecule of asparatate. 8. It is concluded that uptake of dicarboxylic acids by the dicarboxylic acid-transport system is obligatorily coupled to proton uptake such that succinate, malate and fumarate are taken up in electroneutral form and asparate is taken up in cationic form. 9. These results are consistent with, though they do not definitely prove, the energization of succinate uptake of the deltapH.

Aerobiosis↗
PubMed1978

The oxidative activities of membrane vesicles from Bacillus caldolyticus. Energy-dependence of succinate oxidation.

1. The properties of membrane vesicles from the extreme thermophile Bacillus caldolyticus were investigated. 2. Vesicles prepared by exposure of spheroplasts to ultrasound contained cytochromes a, b and c, and at 50 degrees C they rapidly oxidized NADH and ascorbate in the presence of tetramethyl-p-phenylenediamine. Succinate and l-malate were oxidized more slowly, and dl-lactate, l-alanine and glycerol 1-phosphate were not oxidized. 3. In the absence of proton-conducting uncouplers the oxidation of NADH was accompanied by a net translocation of H(+) into the vesicles. Hydrolysis of ATP by a dicyclohexylcarbodi-imide-sensitive adenosine triphosphatase was accompanied by a similarly directed net translocation of H(+). 4. Uncouplers (carbonyl cyanide p-trifluoromethoxyphenylhydrazone or valinomycin plus NH(4) (+)) prevented net H(+) translocation but stimulated ATP hydrolysis, NADH oxidation and ascorbate oxidation. The last result suggested an energy-conserving site in the respiratory chain between cytochrome c and oxygen. 5. Under anaerobic conditions the reduction of cytochrome b by ascorbate (with tetramethyl-p-phenylenediamine) was stimulated by ATP hydrolysis, indicating an energy-conserving site between cytochrome b and cytochrome c. However, no reduction of NAD(+) supported by oxidation of succinate, malate or ascorbate occurred, neither did it with these substrates in the presence of ATP under anaerobic conditions, suggesting that there was no energy-conserving site between NADH and cytochrome b. 6. Succinate oxidation, in contrast with that of NADH and ascorbate, was strongly inhibited by uncouplers and stimulated by ATP hydrolysis. These effects were not observed when phenazine methosulphate, which transfers electrons from succinate dehydrogenase directly to oxygen, was present. It was concluded that in these vesicles the oxidation of succinate was energy-dependent and that the reoxidation of reduced succinate dehydrogenase was dependent on the outward movement of H(+) by the protonmotive force. 7. In support of the foregoing conclusion it was shown that the reduction of fumarate by NADH was an energy-conserving process. 8. If the activities of vesicles accurately represent those of the intact organism it appears that in B. caldolyticus the reduction of fumarate to succinate at the expense of reducing equivalents from NADH is energetically favoured over succinate oxidation even under aerobic conditions. This may be related to the need for an ample supply of succinate for haem synthesis in order to provide cytochromes for the organism.

Adenosine Triphosphate↗
PubMed1975

Oxidation of succinate in heart, brain, and kidney mitochondria in hypobaria and hypoxia.

Exposure of rats to hypobaric stress for periods of up to 36 h caused a consistent change in the succinate-NT reductase activity of the heart mitochondria whereas there was no significant change in the activities of either succinate dehydrogenase and succinate-NT reductase of the brain and the kidney. Mitochondrial succinate dehydrogenase of the heart, the brain and the kidney was activated 2- to 7-fold with the substrate and malonate. The activations obtained with oxalate, citrate and dinitrophenol were relatively lower in comparison to succinate and malonate. Benzohydroquinone and 2-nitrophenol had no stimulatory effect on the heart, the brain and the kidney mitochondria. THE ACTIVATIONS OBTAINED WITH THE VARIOUS EFFECTORS PARTIALLY (OR COMPLETELY IN THE CASE OF SUCCINATE) REVERSED ON WASHING THE MITOCHONDRIAL SAMPLES WITH THE SUCROSE HOMOGENIZING MEDIUM. The effect of ubiquinol, which also activated the enzyme, was only partially reversed after the second preincubation with succinate in the brain and the kidney whereas in the heart the activity was fully reversed. The increased activity of succinate dehydrogenase obtained with ATP and ADP was further enhanced by Mg2+ exclusively in the brain mitochondria, suggesting the possibility of Mg2+-AIP complex as the active species. Succinate-NT reductase of the heart, the brain and the kidney mitochondria showed a high activation with ubiquinone whereas its reduced form had no stimulatory effect.

Adenosine Diphosphate↗
PubMed1977

3-Nitropropionate, the toxic substance of Indigofera, is a suicide inactivator of succinate dehydrogenase.

We have shown that 3-nitropropionate, an isoelectronic analogue of succinate, is a suicide inactivator of succinate dehydrogenase [succinate:(acceptor) oxidoreductase, EC 1.3.99.1] as follows. (i) When rat liver mitochondria oxidize succinate in the presence of 3-nitropropionate carbanion, the rate of O(2) consumption decreases exponentially to a zero value. This pattern is duplicated by subsequent additions of mitochondria. The dependence of the apparent first-order rate constant for enzyme inhibition, as well as the number of enzyme turnovers completed before inhibition, on the concentrations of 3-nitropropionate carbanion and succinate are those expected for an active site-directed and irreversible inhibitor. (ii) The inactivated enzyme is not resuscitated by centrifugation and washing of the mitochondria, in contrast to malonate-treated enzyme, and malonate protects against irreversible, inhibition. (iii) The inhibitor species is 3-nitropropionate carbanion and no external nucleophile is required for inhibition. (iv) The respiratory rates, respiratory control ratios, and ADP/O ratios obtained with NAD-linked substrates are unaffected by 3-nitropropionate carbanion. These results show that 3-nitropropionate carbanion is a highly specific, time-dependent, and irreversible inhibitor of succinate dehydrogenase. By analogy with the reaction of nitroethane with D-amino acid oxidase, the data are consistent with the hypothesis that the carbanionic inhibitor forms a covalent N-5 adduct with the active site flavin. However, the precise mechanism of inactivation, as well as mechanistic extrapolations to the oxidation of succinate, must await the elucidation of the structure of the modified enzyme. We can now explain the toxicity of plants such as Indigofera endecaphylla for mammals and fowl as being due to the irreversible blockage of the Krebs cycle by 3-nitropropionate carbanion.

Animals↗
PubMed1977

Rhodanese-Mediated sulfur transfer to succinate dehydrogenase.

The interaction of the sulfurtransferase rhodanese (EC 2.8.1.1) with succinate dehydrogenase (EC 1.3.99.1), yeast alcohol dehydrogenase (EC 1.1.1.1) and bovine serum albumin was studied. Succinate dehydrogenase incorporates the sulfane sulfur of [35S]rhodanese and, in the presence of unlabelled rhodanese, also incorporates that of [35S]thiosulfate. Rhodanese releases most of its transferable sulfur and is re-loaded in the presence of thiosulfate. Rhodanese undergoes similar modifications with yeast alcohol dehydrogenase but this latter does not bind 35S in amounts comparable to those incorporated in succinate dehydrogenase: nearly all the 35S released by [35S]rhodanese is with low-molecular-weight compounds. Bovine serum albumin also binds very little sulfur and [35S]rhodanese present in the reaction mixture does not discharge its radioactive sulfur nor does it take up sulfur from thiosulfate. Sulfur release from rhodanese appears to depend on the presence of - SH groups in the acceptor protein. Sulfur incorporated into succinate dehydrogenase was analytically determined as sulfide. A comparison of the optical spectra of succinate dehydrogenase preparations incubated with or without rhodanese indicates that there is an effect of the sulfurtransferase on the iron-sulfur absorption of the flavorprotein. The interaction of rhodanese with succinate dehydrogenase greatly decreases the catalytic activity of rhodanese with respect to thiocyanate formation. This is attributed to modifications in rhodanese associated with the reduction of sulfane sulfur to sulfide. Thiosulfate in part protects from this deactivation. The reconstitutive capacity of succinate dehydrogenase increased in parallel with sulfur incorporated in that enzyme following its interaction with rhodanese.

Alcohol Oxidoreductases↗
PubMed1976

Thermodynamic and EPR characteristics of two ferredoxin-type iron-sulfur centers in the succinate-ubiquinone reductase segment of the respiratory chain.

Two distinct ferredosin-type iron-sulfur centers (designated as Centers S-1 and S-2) are present in the soulble succinate dehydrogenase in approximately equivalent concentrations to that of bound flavin. Both Centers S-1 and S-2 exhibit electron paramagnetic resonance absorbance in the reduced state at the same magnetic field (gz = 2.03, gy = 1.93, and gx = 1.91) with similar line shape. Center S-2 is reducible only chemically with dithionite and remains oxidized under physiological conditions. Thus, its functional role is unknown; however, thermodynamic and EPR characterization of this iron-sulfur center has revealed important molecular events related to this dehydrogenase. The midpoint potentials of Centers S-1 and S-2 determined in the soluble succinate dehydrogenase preparations are -5 +/- 15 mV and -400 +/- 15 mV, respectively, while corresponding midpoint potentials determined in particulate preparations, such as succinate-cytochrome c reductase or succinate-ubiquinone reductase, are 0 +/- 15 mV and -260 +/- 15 mV. Reconstitution of soluble succinate dehydrogenase with the cytochrome b-c1 complex is accompanied by a reversion of the Center S-I midpoint from -400 +/- 15 mV to -250 +/- 15 mV with a concomitant restoration of antimycin A-sensitive succinate-cytochrome c reductase activity. There observations indicate that, during the reconstitution process, Center S-I is restored to its original molecular environment. In the reconstitutively active succinate dehydrogenase, the relaxation time of Center S-2 is much shorter than that of S-1, thus Center S-2 spectra are well discernible only below 20 K (at 1 milliwatt of power), while the resonance absorbance of Center S-1 is detectable at higher temperatures and readily saturates below 15 K. Over a wide temperature range the power saturation of Center S-1 resonance absorbance is relieved by Center S-2 in the paramagnetic state, and the Center S-2 central resonance absorbance is broadened by Center S-1 spins, due to a spin-spin interaction between these centers. These observations indicate an adjacent location of these centers in the enzyme molecule. In reconstitutively inactive enzymes, subtle modification of the enzyme structure appears to shift the temperature dependence of Center S-2 relaxation to the higher temperature. Thus the EPR signals of Center S-2 are also detectable at higher temperature. In this system a splitting of the central peak of the Center S-2 spectrum due to spin-spin interaction was observed at extremely low temperatures, while this was not observed in reconstitutively active enzymes or in paritculate preparations. This spin-spin interaction phenomena of inactive enzymes disappeared upon chemical reactivation with concomitant appearance of the reconstitutive activity. These observations provide a close correlation between the molecular integrity of the enzyme and its physiological function.

Animals↗
PubMed1979

Selection of succinic dehydrogenase mutants of Neurospora crassa.

A method is described which permits the selection of mutants of Neurospora crassa that are deficient in succinic dehydrogenase activity. The method relies on the observation that succinic dehydrogenase-deficient strains fail to reduce the dye nitrotetrazolium blue when overlaid with the dye in the presence of succinate and phenazine methosulfate. Wild-type colonies reduced the dye and turned blue, whereas mutant colonies remained colorless. In this communication we present studies of a mutant, SDH-1, isolated by this method. The mutant had 18% of the succinic dehydrogenase activity of the parent strain used in the mutation experiments as determined from the ratio of Vmax activities obtained from Lineweaver-Burk plots. The SDH-1 mutant segregated in a Mendelian manner when back-crossed to its parent strain. Succinate oxidase activity in SDH-1 was low and was markedly inhibited by adenosine 5'-diphosphate. The succinate oxidase activity of the parent strain was high and was not affected by the presence of adenosine 5'-diphosphate.

Mutation↗
PubMed1979

Characterization of a succinate dehydrogenase complex solubilized from the cytoplasmic membrane of Bacillus subtilis with the nonionic detergent Triton X-100.

A succinic dehydrogenase (SDH) complex has been purified from Triton X-100-solubilized membranes from Bacillus subtilis by precipitation with specific antibody. Radioactively labeled precipitated complex was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography of the gels. The complex contained equimolar amounts of three polypeptides with approximate molecular weights of 65,000, 28,000, and 19,000. Five succinic dehydrogenase-negative mutants, belonging to the citF group, contained the 65,000-dalton polypeptide in a soluble form in the cytoplasm. Each 65,000-dalton polypeptide had about one molecule of flavin bound. Another citF mutant, citF11, which lacks the 65,000-dalton polypeptide, contained a membrane-bound 28,000-dalton polypeptide. The wild-type succinic dehydrogenase complex contained cytochrome, probably a cytochrome b. The 19,000-dalton polypeptide is suggested to represent the apoprotein of this cytochrome. The 65,000-dalton and the 28,000-dalton polypeptides are thought to constitute succinic dehydrogenase and to correspond to the flavoprotein and the ironprotein, respectively, as described for succinic dehydrogenase isolated from beef heart mitochondria or Rhodospirillum rubrum chromatophores. The results presented suggest that in B. subtilis succinic dehydrogenase is attached to a cytochrome b in the membrane via the 28,000-dalton (ironprotein) polypeptide.

Bacillus subtilis↗
PubMed1976

Acetate kinase from Veillonella alcalescens. Regulation of enzyme activity by succinate and substrates.

Acetate kinase of Veillonella alcalescens has been shown to be highly regulated enzyme exhibiting two levels of control: the requirement for succinate as a heterotropic allosteric effector, and cooperative binding at the substrate level. Succinate addition was necessary for enzymatic activity in both the direction of acyl phosphate synthesis and that of ATP synthesis. Control at the substrate level was apparent in the cooperative binding (Hill coefficients of 2) of acetyl phosphate, ATP, and ADP. Typical Michaelis kinetic data were observed for succinate (Ka = 20 mM for acetyl phosphate synthesis, 0.4 mM for ATP synthesis), acetate, and propionate. The primary effect of succinate was to increase the apparent Vmax of the enzymatic reaction for the variable substrates, ATP, ADP, and acetyl phosphate. The results are interpreted as evidence that, as a heterotropic effector of the acetate kinase reaction, succinate may regulate levels of propionyl-CoA (produced from propionyl phosphate by action of phosphotransacetylase), a compound required for the conversion of succinate to propionate. Acetase kinase has been shown to be a probable dimeric protein composed of two subunits of molecular weight 44,000 each.

Acetates↗
PubMed1978

The indispensability of phospholipid and ubiquinone in mitochondrial electron transfer from succinate to cytochrome c.

The indispensability of phospholipid and ubiquinone (Q) in mitochondrial electron transfer was studied by depleting phospholipid and Q in succinate-cytochrome c reductase and then replenishing the depleted enzyme. More than 90% of phospholipid and Q was removed by repeated ammonium sulfate-cholate fractionation. The depleted succinate-cytochrome c reductase showed no enzymatic activity for succinate leads to c or QH2 leads to c and yet retained most of the succinate leads to Q activity. All enzymatic activity was restored upon the addition of Q and phospholipid. Restoration required the addition of Q prior to the addition of phospholipid. Reversing the addition sequence or addition of a mixture of phospholipid and Q resulted only in a small restoration of activities. The conditions for restoration are given in detail. Removal of phospholipid from succinate-cytochrome c reductase resulted in reduction of cytochrome c1 in the absence of exogenous electron donor. Replenishing the preparation with phospholipid brought about the reoxidation of cytochrome c1 in the absence of electron acceptor or oxygen.

Animals↗
PubMedDate not supplied

[Reaction ability and alkylation kinetics of sulfhydride groups of soluble succinate dehydrogenase].

Inhibition kinetics of succinate--an acceptor of oxidoreductase activity of soluble succinate dehydrogenase by N-ethylmaleimide is studied. The alkylation reaction is described by the kinetic equation of the first order, its stechiometric coefficient being 1. The binding of enzyme sulphhydride groups by p-chloromercuriumbenzoate blocks the enzyme alkylation and its inhibition by oxaloacetate. Succinate protects succinate dehydrogenase from the inhibitory effect of N-ethylmaleimide. The reaction of the enzyme with an alkylating agent in the presence of different substrate concentrations corresponds kinetically to the model, according to which a sulphhydride group acts in the active site of the enzyme. pKa of this group is 7.0 at 20degreesC. The dependency of the maximal substrate oxidation reaction rate and that of the enzyme alkylation rate on pH coinside at the pH range 5.8--7.8. The presence of anions in the alkylation medium decreases the reaction ability of the active site with respect to N-ethylmaleimide. A mechanism of the initial stage of succinate oxidation with the cooperation of the sulphhydride group of the enzyme active site is postulated.

Binding Sites↗
PubMed1975

Mechanism of the protective effect of succinic semialdehyde and its derivatives in hypoxia.

Preliminary injection of succinic semialdehyde into animals in experiments with hypoxia led to a lower concentration of free ammonia in their brain tissues than in control experiments in which the compound was not given. The enzyme system of the liver tissue catalyzes the oxidation of NAD-H-2 by succinic semialdeyde and its dervitives with a free adelhyde group.The conversion of succinic semialdeyde and its derivatives in the liver tissue leading to the formation of the oxidized form of NAD,which is deficient in hypoxia, and the prevention of accumulation of free ammonia in the brain tissue by preliminary administration of succinic semialdehyde are the possible mechanisms of the antihypoxic properties of succinic semialdehyde and its derivatives.

Aldehydes↗