scholarly journals Control of the citric acid cycle by glyoxylate. The mechanism of inhibition of oxoglutarate dehydrogenase, isocitrate dehydrogenase and aconitate hydratase

1969 ◽  
Vol 114 (3) ◽  
pp. 513-518 ◽  
Author(s):  
A. Adinolfi ◽  
R. Moratti ◽  
S. Olezza ◽  
A. Ruffo
Keyword(s):  
Citric Acid ◽  
Isocitrate Dehydrogenase ◽  
Citric Acid Cycle ◽  
Direct Interaction ◽  
Inhibitory Effect ◽  
Aconitate Hydratase ◽  
Acid Cycle ◽  
Mechanism Of Inhibition ◽  
Oxoglutarate Dehydrogenase ◽  
Thiamin Pyrophosphate

1. The effects of glyoxylate on partially purified preparations of aconitate hydratase, isocitrate dehydrogenase and oxoglutarate dehydrogenase were compared with those of oxalomalate and hydroxyoxoglutarate (obtained by condensation of glyoxylate with oxaloacetate and pyruvate respectively). 2. Glyoxylate (1mm) did not affect aconitate hydratase and isocitrate dehydrogenase, whereas oxalomalate (1mm) inhibited the enzyme activities completely. 3. Glyoxylate (0·025mm) inhibited oxoglutarate dehydrogenase irreversibly, whereas the same concentrations of oxalomalate and hydroxyoxoglutarate were ineffective. This inhibitory effect was prevented if oxoglutarate, pyruvate or oxaloacetate was mixed with the enzyme before the glyoxylate. 4. Incubation of oxoglutarate dehydrogenase with radioactive glyoxylate produced radioactive carbon dioxide; radioactivity was also recovered in the portion of the enzyme identified with thiamin pyrophosphate. 5. The behaviour of glyoxylate in producing multiple inhibitions of the citric acid cycle, either by direct interaction with oxoglutarate dehydrogenase, or by means of its condensation compounds which inhibit aconitate hydratase and isocitrate dehydrogenase, is discussed.

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 Production of tricarballylic acid by rumen microorganisms and its potential toxicity in ruminant tissue metabolism

1986 ◽  
Vol 56 (1) ◽  
pp. 153-162 ◽  
Author(s):  
James B. Russell ◽  
Neil Forsberg
Keyword(s):  
Citric Acid ◽  
Citric Acid Cycle ◽  
Competitive Inhibitor ◽  
Rumen Microorganisms ◽  
Aconitate Hydratase ◽  
Factors Affecting ◽  
Acid Cycle ◽  
Rat Liver Cells ◽  
High Concentrations

1. Rumen microorganisms convert trans-aconitate to tricarballylate. The following experiments describe factors affecting the yield of tricarballylate, its absorption from the rumen into blood and its effect on mammalian citric acid cycle activity in vitro.2. When mixed rumen microorganisms were incubated in vitro with Timothy hay (Phleum praiense L.) and 6.7 mM-trans-aconitate, 64 % of the trans-aconitate was converted to tricarballylate. Chloroform and nirate treatments inhibited methane production and increased the yield of tricarballylate to 82 and 75% respectively.3. Sheep given gelatin capsules filled with 20 g trans-aconitate absorbed tricarballylate and the plasma concentration ranged from 0.3 to 0.5 mM 9 h after administration. Feeding an additional 40 g potassium chloride had little effect on plasma tricarballylate concentrations. Between 9 and 36 h there was a nearly linear decline in plasma tricarballylate.4. Tricarballylate was a competitive inhibitor of the enzyme, aconitate hydratase (aconitase; EC 4.2.1.3), and the inhibitor constant, KI, was 0.52 mM. This KIvalue was similar to the Michaelis-Menten constant (Km) of the enzyme for citrate.5. When liver slices from sheep were incubated with increasing concentrations of tricarballylate, [I4C]acetate oxidation decreased. However, even at relatively high concentrations (8 mM), oxidation was still greater than 80% of the maximum. Oxidation of [I4C]acetate by isolated rat liver cells was inhibited to a greater extent by tricarballylate. Concentrations as low as 0.5 mM caused a 30% inhibition of citric acid cycle activity.

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.

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.

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.

Effect of growth substrate on enzymes of the citric and glyoxylic acid cycles in Thiobacillus novellus

1971 ◽  
Vol 17 (5) ◽  
pp. 617-624 ◽  
Author(s):  
A. Michael Charles
Keyword(s):  
Citric Acid ◽  
High Speed ◽  
Citric Acid Cycle ◽  
Nadh Oxidase ◽  
Specific Activity ◽  
Glyoxylic Acid ◽  
Growth Substrate ◽  
Malic Dehydrogenase ◽  
Aconitate Hydratase ◽  
Acid Cycle

A quantitative study was conducted of enzymes involved in the citric acid cycle and associated systems of the facultative autotroph Thiobacillus novellus grown on five different substrates. Irrespective of the growth substrate the organism possessed complete citric and glyoxylic acid cycles and the specific activity of α-ketoglutarate dehydrogenase was always quite low. Also, the activities of the enzymes of both cycles were usually lowest in extracts from autotrophic cells, and highest in extracts from acetate-grown cells. The three remaining extracts had activities that were between the two extremes with those from glucose-grown cells generally lower than those from pyruvate and succinate. Several exceptions should be noted among these generalizations. For example, the activity of aconitate hydratase and malic dehydrogenase was lowest in extracts from glucose-grown cells while that of isocitric dehydrogenase was lowest in extracts from pyruvate-grown cells. Transhydrogenase activity was virtually absent from extracts of pyruvate- and succinate-grown cells while NADH oxidase, which was identical in these two extracts, was also relatively low. Of interest is the large amount of cytochrome c found in high-speed supernatants. In extracts from autotrophic cells this was about 2.3% of the soluble protein and is suggestive of a significant role being played by the electron-transport system during growth of the organism.

scholarly journals Isocitrate Dehydrogenase of Bradyrhizobium japonicum Is Not Required for Symbiotic Nitrogen Fixation with Soybean

2006 ◽  
Vol 188 (21) ◽  
pp. 7600-7608 ◽  
Author(s):  
Ritu Shah ◽  
David W. Emerich
Keyword(s):  
Nitrogen Fixation ◽  
Citric Acid ◽  
Dehydrogenase Activity ◽  
Mutant Strain ◽  
Isocitrate Dehydrogenase ◽  
Bradyrhizobium Japonicum ◽  
Citric Acid Cycle ◽  
Symbiotic Nitrogen Fixation ◽  
Nodule Development ◽  
Acid Cycle

ABSTRACT A mutant strain of Bradyrhizobium japonicum USDA110 lacking isocitrate dehydrogenase activity was created to determine whether this enzyme was required for symbiotic nitrogen fixation with soybean (Glycine max cv. Williams 82). The isocitrate dehydrogenase mutant, strain 5051, was constructed by insertion of a streptomycin resistance gene cassette. The mutant was devoid of isocitrate dehydrogenase activity and of immunologically detectable protein, indicating there is only one copy in the genome. Strain 5051 grew well on a variety of carbon sources, including arabinose, pyruvate, succinate, and malate, but, unlike many microorganisms, was a glutamate auxotroph. Although the formation of nodules was slightly delayed, the mutant was able to form nodules on soybean and reduce atmospheric dinitrogen as well as the wild type, indicating that the plant was able to supply sufficient glutamate to permit infection. Combined with the results of other citric acid cycle mutants, these results suggest a role for the citric acid cycle in the infection and colonization stage of nodule development but not in the actual fixation of atmospheric dinitrogen.

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