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

1976 ◽  
Vol 154 (3) ◽  
pp. 689-700 ◽  
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.

scholarly journals Activities of citrate synthase, NAD+-linked and NADP+-linked isocitrate dehydrogenases, glutamate dehydrogenase, aspartate aminotransferase and alanine aminotransferase in nervous tissues from vertebrates and invertebrates

1975 ◽  
Vol 150 (1) ◽  
pp. 105-111 ◽  
Author(s):  
P H Sugden ◽  
E A Newsholme
Keyword(s):  
Citric Acid ◽  
Glutamate Dehydrogenase ◽  
Isocitrate Dehydrogenase ◽  
Aspartate Aminotransferase ◽  
Alanine Aminotransferase ◽  
Nervous Tissue ◽  
Citric Acid Cycle ◽  
Citrate Synthase ◽  
Acid Cycle ◽  
Dehydrogenase Reaction

1. The activities of citrate synthase and NAD+-linked and NADP+-linked isocitrate dehydrogenases were measured in nervous tissue from different animals in an attempt to provide more information about the citric acid cycle in this tissue. In higher animals the activities of citrate synthase are greater than the sum of activities of the isocitrate dehydrogenases, whereas they are similar in nervous tissues from the lower animals. This suggests that in higher animals the isocitrate dehydrogenase reaction is far-removed from equilibrium. If it is assumed that isocitrate dehydrogenase activities provide an indication of the maximum flux through the citric acid cycle, the maximum glycolytic capacity in nervous tissue is considerably greater than that of the cycle. This suggest that glycolysis can provide energy in excess of the aerobic capacity of the tissue. 2. The activities of glutamate dehydrogenase are high in most nervous tissues and the activities of aspartate aminotransferase are high in all nervous tissue investigated. However, the activities of alanine aminotransferase are low in all tissues except the ganglia of the waterbug and cockroach. In these insect tissues, anaerobic glycolysis may result in the formation of alanine rather than lactate.

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

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.

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

2006 ◽  
Vol 188 (12) ◽  
pp. 4350-4355 ◽  
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.

scholarly journals Lipotoxic Palmitate Impairs the Rate of β-Oxidation and Citric Acid Cycle Flux in Rat Neonatal Cardiomyocytes

2016 ◽  
Vol 40 (5) ◽  
pp. 969-981 ◽  
Author(s):  
Taha Haffar ◽  
Ali Akoumi ◽  
Nicolas Bousette
Keyword(s):  
Fatty Acid ◽  
Citric Acid ◽  
Dehydrogenase Activity ◽  
Fatty Acid Oxidation ◽  
Isocitrate Dehydrogenase ◽  
Lipid Accumulation ◽  
Citric Acid Cycle ◽  
Acid Oxidation ◽  
Acid Cycle ◽  
Neonatal Cardiomyocytes

Background/Aims: Diabetic hearts exhibit intracellular lipid accumulation. This suggests that the degree of fatty acid oxidation (FAO) in these hearts is insufficient to handle the elevated lipid uptake. We previously showed that palmitate impaired the rate of FAO in primary rat neonatal cardiomyocytes. Here we were interested in characterizing the site of FAO impairment induced by palmitate since it may shed light on the metabolic dysfunction that leads to lipid accumulation in diabetic hearts. Methods: We measured fatty acid oxidation, acetyl-CoA oxidation, and carnitine palmitoyl transferase (Cpt1b) activity. We measured both forward and reverse aconitase activity, as well as NAD+ dependent isocitrate dehydrogenase activity. We also measured reactive oxygen species using the 2', 7'-Dichlorofluorescin Diacetate (DCFDA) assay. Finally we used thin layer chromatography to assess diacylglycerol (DAG) levels. Results: We found that palmitate significantly impaired mitochondrial β-oxidation as well as citric acid cycle flux, but not Cpt1b activity. Palmitate negatively affected net aconitase activity and isocitrate dehydrogenase activity. The impaired enzyme activities were not due to oxidative stress but may be due to DAG mediated PKC activation. Conclusion: This work demonstrates that palmitate, a highly abundant fatty acid in human diets, causes impaired β-oxidation and citric acid cycle flux in primary neonatal cardiomyocytes. This metabolic defect occurs prior to cell death suggesting that it is a cause, rather than a consequence of palmitate mediated lipotoxicity. This impaired mitochondrial metabolism can have important implications for metabolic diseases such as diabetes and obesity.

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

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.

scholarly journals 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

1979 ◽  
Vol 178 (1) ◽  
pp. 209-216 ◽  
Author(s):  
Andrew N. Rowan ◽  
Eric A. Newsholme
Keyword(s):  
Citric Acid ◽  
Citric Acid Cycle ◽  
Flight Muscle ◽  
Citrate Synthase ◽  
Adenine Nucleotides ◽  
Total Content ◽  
Acetyl Coa ◽  
Free Concentration ◽  
Acid Cycle ◽  
Early Stages

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.

Citric acid cycle enzymes and nitrogenase in nodules of Pisum sativum

1977 ◽  
Vol 23 (9) ◽  
pp. 1197-1200 ◽  
Author(s):  
W. G. W. Kurz ◽  
T. A. LaRue
Keyword(s):  
Nitrogen Fixation ◽  
Citric Acid ◽  
Pisum Sativum ◽  
Isocitrate Dehydrogenase ◽  
Citric Acid Cycle ◽  
Acid Cycle ◽  
Isocitric Dehydrogenase ◽  
Citric Acid Cycle Enzymes

Activity of isocitric dehydrogenase (isocitrate dehydrogenase (NADP+); EC 1.1.1.42) in bacterids is highest at the time of maximum nitrogen fixation. It is likely that isocitric dehydrogenase is the source of reductant fordinitrogen fixation.

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

1973 ◽  
Vol 51 (6) ◽  
pp. 849-854 ◽  
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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