Changes in the contents of adenine nucleotides and intermediates of glycolysis and citric acid cycle in flight muscle of the locust upon flight and their relationship to the control of the cycle

1. The contents of some intermediates of glycolysis, the citric acid cycle and adenine nucleotides have been measured in the freeze-clamped locust flight muscle at rest and after 10s and 3min flight. The contents of glucose 6-phosphate, pyruvate, alanine and especially fructose bisphosphate and triose phosphates increased markedly upon flight. The content of acetyl-CoA is decreased after 3min flight whereas that of acetylcarnitine is decreased markedly after 10s flight, but returns towards the resting value after 3min flight. The content of citrate is markedly decreased after both 10s and 3min flight, whereas that of isocitrate is changed very little after 10s and is increased by 50% after 3min. The content of oxaloacetate is very low in insect flight muscle and hence it was measured by a sensitive radiochemical assay. The content of oxaloacetate increased about 2-fold after 3min flight. A similar change was observed in the content of malate. The content of ATP decreased about 15%, whereas those of ADP and AMP increased about 2-fold after 3min flight. 2. Calculations based on O2 uptake of the intact insect indicate that the rate of the citric acid cycle must be increased >100-fold during flight. Consequently, if citrate synthase catalyses a non-equilibrium reaction, the activity of the enzyme must increase >100-fold during flight. However, changes in the concentrations of possible regulators of citrate synthase, oxaloacetate, acetyl-CoA and citrate (which is an allosteric inhibitor), are not sufficient to account for this change in activity. It is concluded that there may be much larger changes in the free concentration of oxaloacetate than are indicated by the changes in the total content of this metabolite or that other unknown factors must play an additional role in the regulation of citrate synthase activity. 3. The increased content of oxaloacetate could be produced via pyruvate carboxylase, which may be stimulated during the early stages of flight by the increased concentration of pyruvate. 4. The decreases in the concentrations of citrate and α-oxoglutarate indicate that isocitrate dehydrogenase and oxoglutarate dehydrogenase may be stimulated by factors other than their pathway substrates during the early stages of flight. 5. Calculated mitochondrial and cytosolic NAD+/NADH ratios are both increased upon flight. The change in the mitochondrial ratio indicates the importance of the intramitochondrial ATP/ADP concentration ratio in the regulation of the rate of electron transfer in this muscle.

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The activities of the citric acid-cycle enzymes in rat bone-marrow cells

Biochemical Journal ◽

10.1042/bj1080413 ◽

1968 ◽

Vol 108 (3) ◽

pp. 413-415

Author(s):

Eugene Goldwasser

Keyword(s):

Bone Marrow ◽

Citric Acid ◽

Citric Acid Cycle ◽

Citrate Synthase ◽

Bone Marrow Cells ◽

Mitochondrial Enzymes ◽

Acid Cycle ◽

Citric Acid Cycle Enzymes ◽

Rat Bone ◽

Marrow Cells

The activities of the eight citric acid-cycle enzymes of rat bone-marrow cells were determined along with several other mitochondrial and non-mitochondrial enzymes. Four of the citric acid-cycle enzymes (aconitase, succinyl-CoA thiokinase, α-oxoglutarate dehydrogenase and succinate dehydrogenase) have closely similar low activities; two [isocitrate dehydrogenase (NAD) and citrate synthase] have intermediate activities; the remaining two (malate dehydrogenase and fumarase) have high activities. The other enzymes surveyed also exhibited a spread of three orders of magnitude, the mitochondrial enzymes showing no less variation than the others.

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Activities of citrate synthase and NAD+-linked and NADP+-linked isocitrate dehydrogenase in muscle from vertebrates and invertebrates

Biochemical Journal ◽

10.1042/bj1540689 ◽

1976 ◽

Vol 154 (3) ◽

pp. 689-700 ◽

Cited By ~ 247

Author(s):

P R. Alp ◽

E A. Newsholme ◽

V A. Zammit

Keyword(s):

Citric Acid ◽

Isocitrate Dehydrogenase ◽

Citric Acid Cycle ◽

Citrate Synthase ◽

Insect Flight ◽

Mechanical Activity ◽

Activity Data ◽

Acid Cycle ◽

Equilibrium Reaction ◽

Flight Muscles

1. The activities of citrate synthase, NAD+-linked and NADP+-linked isocitrate dehydrogenase were measured in muscles from a large number of animals, in order to provide some indication of the importance of the citric acid cycle in these muscles. According to the differences in enzyme activities, the muscles can be divided into three classes. First, in a number of both vertebrate and invertebrate muscles, the activities of all three enzymes are very low. It is suggested that either the muscles use energy at a very low rate or they rely largely on anaerobic glycolysis for higher rates of energy formation. Second, most insect flight muscles contain high activities of citrate synthase and NAD+-linked isocitrate dehydrogenase, but the activities of the NADP+-linked enzyme are very low. The high activities indicate the dependence of insect flight on energy generated via the citric acid cycle. The flight muscles of the beetles investigated contain high activities of both isocitrate dehydrogenases. Third, other muscles of both vertebrates and invertebrates contain high activities of citrate synthase and NADP+-liniked isocitrate dehydrogenase. Many, if not all, of these muscles are capable of sustained periods of mechanical activity (e.g. heart muscle, pectoral muscles of some birds). Consequently, to support this activity fuel must be supplied continually to the muscle via the circulatory system which, in most animals, also transports oxygen so that energy can be generated by complete oxidation of the fuel. It is suggested that the low activities of NAD+-linked isocitrate dehydrogenase in these muscles may be involved in oxidation of isocitrate in the cycle when the muscles are at rest. 2. A comparison of the maximal activities of the enzymes with the maximal flux through the cycle suggests that, in insect flight muscle, NAD+-linked isocitrate dehydrogenase catalyses a non-equilibrium reaction and citrate synthease catalyses a near-equilibrium reaction. In other muscles, the enzyme-activity data suggest that both citrate synthase and the isocitrate dehydrogenase reactions are near-equilibrium.

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Probing the Origin of Acetyl-CoA and Oxaloacetate Entering the Citric Acid Cycle from the13C Labeling of Citrate Released by Perfused Rat Hearts

Journal of Biological Chemistry ◽

10.1074/jbc.272.42.26117 ◽

1997 ◽

Vol 272 (42) ◽

pp. 26117-26124 ◽

Cited By ~ 43

Author(s):

Blandine Comte ◽

Geneviève Vincent ◽

Bertrand Bouchard ◽

Christine Des Rosiers

Keyword(s):

Citric Acid ◽

Citric Acid Cycle ◽

Acetyl Coa ◽

Acid Cycle ◽

Rat Hearts ◽

Perfused Rat Hearts

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Metabolism of [3-13C]pyruvate and [3-13C]propionate in normal and ischaemic rat heart in vivo: 1H- and 13C-NMR studies

Biochemical Journal ◽

10.1042/bj3120075 ◽

1995 ◽

Vol 312 (1) ◽

pp. 75-81 ◽

Cited By ~ 17

Author(s):

B Sumegi ◽

B Podanyi ◽

P Forgo ◽

K E Kover

Keyword(s):

Citric Acid ◽

13C Nmr ◽

Rat Heart ◽

Citric Acid Cycle ◽

Nmr Studies ◽

Acetyl Coa ◽

1H And 13C Nmr ◽

Acid Cycle ◽

Propionyl Carnitine

The oxidation of [3-13C]pyruvate and [3-13C]propionate was studied in vivo in infused rats. The infused [3-13C]pyruvate was quickly converted to [3-13C]lactate in the blood, and the [3-13C]lactate formed was well metabolized in both normoxic and ischaemic hearts. Large differences (200-600%) in the 13C enrichment of alanine (C-3) and acetyl-CoA (C-2) compared with lactate (C-3) were found in both normoxic and ischaemic hearts, suggesting that the extracellular [3-13C]lactate preferentially entered a region of the cytoplasm which specifically transfers the labelled pyruvate (formed from [3-13C]lactate) to the mitochondria. The highly enriched mitochondrial pyruvate gave high enrichment in alanine and acetyl-CoA, which was detected by 1H- and 13C-NMR spectroscopy. Ischaemia increased 13C incorporation into the main cytoplasmic lactate pool and decreased 13C incorporation into citric acid cycle intermediates, mainly decreasing the pyruvate anaplerosis. Isoprenaline-induced ischaemia of the heart caused only a slight decrease in pyruvate oxidation. In contrast to the decreased anaplerosis of pyruvate, the anaplerosis of propionate (and propionyl-carnitine) increased significantly in ischaemic hearts, which may contribute to the protective effect of propionyl-carnitine seen in ischaemia. In addition, we found that [3-13C]propionate preferentially labelled aspartate C-3 in rat heart, suggesting incomplete randomization of label in the succinyl-CoA-malate span of the citric acid cycle. These data show that proton observed 13C edited spectroscopic methods, i.e. heteronuclear spin-echo and the one-dimensional heteronuclear multiple quantum coherence sequence, can be successfully used to study heart metabolism in vivo.

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Carbon Isotope Fractionation by Autotrophic Bacteria with Three Different C02 Fixation Pathways

Zeitschrift für Naturforschung C ◽

10.1515/znc-1989-5-610 ◽

1989 ◽

Vol 44 (5-6) ◽

pp. 397-402 ◽

Cited By ~ 82

Author(s):

Andrea Preuß ◽

Rolf Schauder ◽

Georg Fuchs ◽

Willibald Stichler

Keyword(s):

Citric Acid ◽

Carbon Isotope ◽

Isotope Fractionation ◽

Citric Acid Cycle ◽

Pentose Phosphate ◽

Acetobacterium Woodii ◽

Acetyl Coa ◽

Acid Cycle ◽

Acetyl Coa Pathway ◽

Cell Carbon

Abstract Carbon isotope fractionation during autotrophic growth o f different bacteria which possess different autotrophic CO2 fixation pathways has been studied. 13C /12C -Ratios in the cell carbon of the following bacteria were determined (CO2 fixation pathway suggested or proven in parentheses): Alkaligenes eutrophus (reductive pentose phosphate cycle), Desulfobacterium autotrophicum and Acetobacterium woodii (reductive acetyl-CoA pathway), Desulfobacter hydrogenophilus and Thermoproteus neutrophilus (reductive citric acid cycle). The Δδ13C values, which indicate the per mille deviation of the 13C content of cell carbon from that of the CO : used as the sole carbon source, range from - 10%° (reductive citric acid cycle) over - 26%° (reductive pentose phosphate cycle) to -36%° (reductive acetyl-CoA pathway). Acetate formed via the acetyl-CoA pathway by the acetogenic Acetobacterium woodii showed a Δδ13C = -40%°. These data are discussed in view of the different CO2 fixation reactions used by the bacteria and especially with regard to the isotopic composition of sedimentary carbon through time.

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Citric Acid Cycle in the Hyperthermophilic Archaeon Pyrobaculum islandicum Grown Autotrophically, Heterotrophically, and Mixotrophically with Acetate

Journal of Bacteriology ◽

10.1128/jb.00138-06 ◽

2006 ◽

Vol 188 (12) ◽

pp. 4350-4355 ◽

Cited By ~ 27

Author(s):

Yajing Hu ◽

James F. Holden

Keyword(s):

Citric Acid ◽

Yeast Extract ◽

Growth Rates ◽

Citric Acid Cycle ◽

Citrate Synthase ◽

Autotrophic Growth ◽

Acid Cycle ◽

Hyperthermophilic Archaeon ◽

Citrate Lyase ◽

Pyrobaculum Islandicum

ABSTRACT The hyperthermophilic archaeon Pyrobaculum islandicum uses the citric acid cycle in the oxidative and reductive directions for heterotrophic and autotrophic growth, respectively, but the control of carbon flow is poorly understood. P. islandicum was grown at 95°C autotrophically, heterotrophically, and mixotrophically with acetate, H2, and small amounts of yeast extract and with thiosulfate as the terminal electron acceptor. The autotrophic growth rates and maximum concentrations of cells were significantly lower than those in other media. The growth rates on H2 and 0.001% yeast extract with and without 0.05% acetate were the same, but the maximum concentration of cells was fourfold higher with acetate. There was no growth with acetate if 0.001% yeast extract was not present, and addition of H2 to acetate-containing medium greatly increased the growth rates and maximum concentrations of cells. P. islandicum cultures assimilated 14C-labeled acetate in the presence of H2 and yeast extract with an efficiency of 55%. The activities of 11 of 19 enzymes involved in the central metabolism of P. islandicum were regulated under the three different growth conditions. Pyruvate synthase and acetate:coenzyme A (CoA) ligase (ADP-forming) activities were detected only in heterotrophically grown cultures. Citrate synthase activity decreased in autotrophic and acetate-containing cultures compared to the activity in heterotrophic cultures. Acetylated citrate lyase, acetate:CoA ligase (AMP forming), and phosphoenolpyruvate carboxylase activities increased in autotrophic and acetate-containing cultures. Citrate lyase activity was higher than ATP citrate synthase activity in autotrophic cultures. These data suggest that citrate lyase and AMP-forming acetate:CoA ligase, but not ATP citrate synthase, work opposite citrate synthase to control the direction of carbon flow in the citric acid cycle.

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Rethinking the Citric Acid Cycle: Connecting Pyruvate Carboxylase and Citrate Synthase to the Flow of Energy and Material

International Journal of Molecular Sciences ◽

10.3390/ijms22020604 ◽

2021 ◽

Vol 22 (2) ◽

pp. 604

Author(s):

Dirk Roosterman ◽

Graeme Stuart Cottrell

Keyword(s):

Lactate Dehydrogenase ◽

Citric Acid ◽

Pyruvate Carboxylase ◽

Citric Acid Cycle ◽

Citrate Synthase ◽

Monocarboxylate Transporter ◽

Acid Cycle ◽

Oxaloacetic Acid ◽

Monocarboxylate Transporter 1 ◽

Original Concept

In 1937, Sir H. A Krebs first published the Citric Acid Cycle, a unidirectional cycle with carboxylic acids. The original concept of the Citric Acid Cycle from Krebs’ 1953 Nobel Prize lecture illustrates the unidirectional degradation of lactic acid to water, carbon dioxide and hydrogen. Here, we add the heart lactate dehydrogenase•proton-linked monocarboxylate transporter 1 complex, connecting the original Citric Acid Cycle to the flow of energy and material. The heart lactate dehydrogenase•proton-linked monocarboxylate transporter 1 complex catalyses the first reaction of the Citric Acid Cycle, the oxidation of lactate to pyruvate, and thus secures the provision of pyruvic acid. In addition, we modify Krebs’ original concept by feeding the cycle with oxaloacetic acid. Our concept enables the integration of anabolic processes and allows adaption of the organism to recover ATP faster.

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Differences between mouse and rat pancreatic islets: succinate responsiveness, malic enzyme, and anaplerosis

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00041.2002 ◽

2002 ◽

Vol 283 (2) ◽

pp. E302-E310 ◽

Cited By ~ 44

Author(s):

Michael J. MacDonald

Keyword(s):

Citric Acid ◽

Pancreatic Islets ◽

Insulin Release ◽

Malic Enzyme ◽

Citric Acid Cycle ◽

Acetyl Coa ◽

Acid Cycle ◽

Rat Islets ◽

Rat Pancreatic Islets ◽

Mouse Islets

Succinic acid methyl esters are potent insulin secretagogues in rat pancreatic islets, but they do not stimulate insulin release in mouse islets. Unlike rat and human islets, mouse islets lack malic enzyme and, therefore, are unable to form pyruvate from succinate-derived malate for net synthesis of acetyl-CoA. Dimethyl-[2,3-14C]succinate is metabolized in the citric acid cycle in mouse islets to the same extent as in rat islets, indicating that endogenous acetyl-CoA condenses with oxaloacetate derived from succinate. However, without malic enzyme, the net synthesis from succinate of the citric acid cycle intermediates citrate, isocitrate, and α-ketoglutarate cannot occur. Glucose and other nutrients that augment α-ketoglutarate formation are secretagogues in mouse islets with potencies similar to those in rat islets. All cycle intermediates can be net-synthesized from α-ketoglutarate. Rotenone, an inhibitor of site I of the electron transport chain, inhibits methyl succinate-induced insulin release in rat islets even though succinate oxidation forms ATP at sites II and III of the respiratory chain. Thus generating ATP, NADH, and anaplerosis of succinyl-CoA plus the four-carbon dicarboxylic acids of the cycle and its metabolism in the citric acid cycle is insufficient for a fuel to be insulinotropic; it must additionally promote anaplerosis of α-ketoglutarate or two intermediates interconvertible with α-ketoglutarate, citrate, and isocitrate.

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Effects of Exercise, Training, and Diet on Muscle Citric Acid Cycle Enzyme Activity

Canadian Journal of Biochemistry ◽

10.1139/o73-105 ◽

1973 ◽

Vol 51 (6) ◽

pp. 849-854 ◽

Cited By ~ 37

Author(s):

G. Lynis Dohm ◽

Richard L. Huston ◽

E. Wayne Askew ◽

H. Lee Fleshood

Keyword(s):

Citric Acid ◽

Citric Acid Cycle ◽

Citrate Synthase ◽

Exhaustive Exercise ◽

High Fat ◽

Acid Cycle ◽

Cycle Enzyme ◽

High Fat Diets ◽

Citric Acid Cycle Enzymes ◽

Fat Diets

The effects of training, exhaustive exercise, and diet on the activity of skeletal muscle citric acid cycle enzymes were studied. Training increased the activities of all cycle enzymes. Exhaustion of trained rats resulted in lowered activities of NAD-specific isocitrate dehydrogenase, succinate dehydrogenase, and cytochrome oxidase but citrate synthase and malate dehydrogenase were unaffected. The enzyme activities in untrained muscle were not changed by exhaustive exercise. High carbohydrate and high fat diets did not alter citric acid cycle activities in trained rested or untrained rested rats and did not moderate or accentuate the effects of exhaustive exercise. The results indicate that muscle citric acid cycle activity is increased by training and decreased by exhaustion of trained animals.

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