scholarly journals The mechanisms of reductive carboxylation reactions. Carbon dioxide or bicarbonate as substrate of nicotinamide-adenine dinucleotide phosphate-linked isocitrate dehydrogenase and ‘malic’ enzyme

1968 ◽  
Vol 110 (2) ◽  
pp. 223-230 ◽  
Author(s):  
K. Dalziel ◽  
J. C. Londesborough
Keyword(s):  
Carbon Dioxide ◽  
Isocitrate Dehydrogenase ◽  
Malic Enzyme ◽  
Time Course ◽  
Kinetic Method ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Quantitative Agreement ◽  
Effects Of Ph ◽  
Reductive Carboxylation ◽  
Primary Substrate

1. A simple kinetic method was devised to show whether dissolved CO2 or HCO3– ion is the substrate in enzyme-catalysed carboxylation reactions. 2. The time-course of the reductive carboxylation of 2-oxoglutarate by NADPH, catalysed by isocitrate dehydrogenase, was studied by a sensitive fluorimetric method at pH7·3 and pH6·4, with large concentrations of substrate and coenzyme and small carbon dioxide concentrations. 3. Reaction was initiated by the addition of carbon dioxide in one of three forms: (i) as the dissolved gas in equilibrium with bicarbonate; (ii) as unbuffered bicarbonate solution; (iii) as the gas or as an unbuffered solution of the gas in water. Different progress curves were obtained in the three cases. 4. The results show that dissolved CO2 is the primary substrate of the enzyme, and that HCO3– ion is at best a very poor substrate. The progress curves are in quantitative agreement with this conclusion and with the known rates of the reversible hydration of CO2 under the conditions of the experiments. The effects of carbonic anhydrase confirm the conclusions. 5. Similar experiments on the reductive carboxylation of pyruvate catalysed by the ‘malic’ enzyme show that dissolved CO2 is the primary substrate of this enzyme also. 6. The results are discussed in relation to the mechanisms of these enzymes, and the effects of pH on the reactions. 7. The advantages of the method and its possible applications to other enzymes involved in carbon dioxide metabolism are discussed.

scholarly journals The nature of carbon dioxide substrate and equilibrium constant of the 6-phosphogluconate dehydrogenase reaction

1969 ◽  
Vol 115 (4) ◽  
pp. 633-638 ◽  
Author(s):  
R. H. Villet ◽  
K. Dalziel
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Equilibrium Constant ◽  
Heat Of Reaction ◽  
Phosphogluconate Dehydrogenase ◽  
Sheep Liver ◽  
Dehydrogenase Reaction ◽  
Reductive Carboxylation ◽  
Primary Substrate

1. It was shown that dissolved CO2 and not HCO3− or H2CO3 is the primary substrate for reductive carboxylation with 6-phosphogluconate dehydrogenase from sheep liver. 2. The equilibrium constant of the reaction was measured in solutions of various ionic strengths and at several temperatures, and the free energy and heat of reaction were determined.

Characteristics of the canopy, root system and grain yield of a crop of Lupinus angustifolius cv. Unicrop

1975 ◽  
Vol 26 (3) ◽  
pp. 497 ◽  
Author(s):  
EAN Greenwood ◽  
P Farrington ◽  
JD Beresford
Keyword(s):  
Carbon Dioxide ◽  
Grain Yield ◽  
Leaf Area ◽  
Time Course ◽  
Dry Weight ◽  
Grain Filling ◽  
Main Axis ◽  
Carbon Dioxide Exchange ◽  
Area Index ◽  
Plant Parts

The time course of development of a lupin crop was studied at Bakers Hill, Western Australia. The aim was to gain insight into the crop factors influencing yield. Weekly measurements were made of numbers and weights of plant parts, and profiles of roots, leaf area and light interception. A profile of carbon dioxide in the crop atmosphere was taken at the time of maximum leaf area, and the net carbon dioxide exchange (NCE) of pods was estimated for three successive weeks. The crop took 10 weeks to attain a leaf area index (LAI) of 1 and a further 9 weeks to reach a maximum LAI of 3.75, at which time only 33% of daylight reached the pods on the main axis. Once the maximum LAI was attained at week 19, leaf fall accelerated and rapid grain filling commenced almost simultaneously on all of the three orders of axes which had formed pods. Measurements of NCE between pods on the main axis and the air suggest that the assimilation of external carbon dioxide by the pods contributed little to grain filling. Grain dry weight was 2100 kg ha-1 of which 30%, 60% and 10% came from the main axis, first and second order apical axes respectively. Only 23% of the flowers set pods and this constitutes an important physiological limitation to grain yield.

scholarly journals Heterozygosity of the Sheep: Polymorphism of ?Malic Enzyme?, Isocitrate Dehydrogenase (NADP+), Catalase and Esterase

1977 ◽  
Vol 30 (2) ◽  
pp. 127 ◽  
Author(s):  
CM Ann Baker ◽  
Clyde Manwell
Keyword(s):  
Isocitrate Dehydrogenase ◽  
Malic Enzyme ◽  
Enzyme Variation

In contrast to other reports, it is found that the sheep has approximately as much enzyme variation as man.

Quantum Yields of Photosystem II Electron Transport and Carbon Dioxide Fixation in C4 Plants

1990 ◽  
Vol 17 (5) ◽  
pp. 579 ◽  
Author(s):  
JP Krall ◽  
GE Edwards
Keyword(s):  
Carbon Dioxide ◽  
Electron Transport ◽  
Quantum Yield ◽  
Photosystem Ii ◽  
Malic Enzyme ◽  
Co2 Fixation ◽  
C4 Plants ◽  
Quantum Yields ◽  
Ps Ii ◽  
Co2 Concentrations

The quantum yields of non-cyclic electron transport from photosystem II (determined from chlorophyll a fluorescence) and carbon dioxide assimilation were measured in vivo in representative species of the three subgroups of C4 plants (NADP-malic enzyme, NAD-malic enzyme and PEP-carboxykinase) over a series of intercellular CO2 concentrations (CI) at both 21% and 2% O2. The CO2 assimilation rate was independent of O2 concentration over the entire range of Ci (up to 500 μbar) in all three C4 subgroups. The quantum yield of PS II electron transport was similar, or only slightly greater, in 21% v. 2% O2 at all Ci values. In contrast, in the C3 species wheat there was a large O2 dependent increase in PS II quantum yield at low CO2, which reflects a high level of photorespiration. In the C4 plants, the relationship of the quantum yield of PS II electron transport to the quantum yield of CO2 fixation is linear suggesting that photochemical use of energy absorbed by PS II is tightly linked to CO2 fixation in C4 plants. This relationship is nearly identical in all three subgroups and may allow estimates of photosynthetic rates of C4 plants based on measurements of PS II photochemical efficiency. The results suggest that in C4 plants both the photoreduction of O2 and photorespiration are low, even at very limiting CO2 concentrations.

scholarly journals The metabolism of glyoxylate by cell-free extracts of Pseudomonas sp

1966 ◽  
Vol 101 (3) ◽  
pp. 755-763 ◽  
Author(s):  
E Bailey ◽  
RP Hullin
Keyword(s):  
Carbon Dioxide ◽  
Isocitrate Dehydrogenase ◽  
Coenzyme A ◽  
Pseudomonas Sp ◽  
Reaction Products ◽  
Acetyl Coenzyme A ◽  
Acetyl Coenzyme ◽  
Oxoglutarate Dehydrogenase

1. Extracts of Pseudomonas sp. grown on butane-2,3-diol oxidized glyoxylate to carbon dioxide, some of the glyoxylate being reduced to glycollate in the process. The oxidation of malate and isocitrate, but not the oxidation of pyruvate, can be coupled to the reduction of glyoxylate to glycollate by the extracts. 2. Extracts of cells grown on butane-2,3-diol decarboxylated oxaloacetate to pyruvate, which was then converted aerobically or anaerobically into lactate, acetyl-coenzyme A and carbon dioxide. The extracts could also convert pyruvate into alanine. However, pyruvate is not an intermediate in the metabolism of glyoxylate since no lactate or alanine could be detected in the reaction products and no labelled pyruvate could be obtained when extracts were incubated with [1-(14)C]glyoxylate. 3. The (14)C was incorporated from [1-(14)C]glyoxylate by cell-free extracts into carbon dioxide, glycollate, glycine, glutamate and, in trace amounts, into malate, isocitrate and alpha-oxoglutarate. The (14)C was initially incorporated into isocitrate at the same rate as into glycine. 4. The rate of glyoxylate utilization was increased by the addition of succinate, alpha-oxoglutarate or citrate, and in each case alpha-oxoglutarate became labelled. 5. The results are consistent with the suggestion that the carbon dioxide arises by the oxidation of glyoxylate via reactions catalysed respectively by isocitratase, isocitrate dehydrogenase and alpha-oxoglutarate dehydrogenase.

scholarly journals Equilibrium binding of coenzymes and substrates to nicotinamide-adenine dinucleotide phosphate-linked isocitrate dehydrogenase from bovine heart mitochondria

1978 ◽  
Vol 171 (3) ◽  
pp. 733-742 ◽  
Author(s):  
C H Reynolds ◽  
P W Kuchel ◽  
K Dalziel
Keyword(s):  
Ionic Strength ◽  
Isocitrate Dehydrogenase ◽  
Binding Capacity ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Kinetic Properties ◽  
Protein Fluorescence ◽  
Fluorescence Measurements ◽  
Equilibrium Binding ◽  
Maximum Binding Capacity ◽  
Fluorescence Titrations

1. The stoicheiometries and affinities of ligand binding to isocitrate dehydrogenase were studied at pH 7.0, mainly by measuring changes in NADPH and protein fluorescence. 2. The affinity of the enzyme for NADPH is about 100-fold greater than it is for NADP+ in various buffer/salt solutions, and the affinities for both coenzymes are decreased by Mg2+, phosphate and increase in ionic strength. 3. The maximum binding capacity of the dimeric enzyme for NADPH, from coenzyme fluorescence and protein-fluorescence measurements, and also for NADP+, by ultrafiltration, is 2 mol/mol of enzyme. Protein-fluorescence titrations of the enzyme with NADP+ are apparently inconsistent with this conclusion, indicating that the increase in protein fluorescence caused by NADP+ binding is not proportional to fractional saturation of the binding sites. 4. Changes in protein fluorescence caused by changes in ionic strength and by the binding of substrates, Mg2+ or NADP+ (but not NADPH) are relatively slow, suggesting conformation changes. 5. In the presence of Mg2+, the enzyme binds isocitrate very strongly, and 2-oxoglutarate rather weakly. 6. Evidence is presented for the formation of an abortive complex of enzyme-Mg2+-isocitrate-NADPH in which isocitrate and NADPH are bound much more weakly than in their complexes with enzyme and Mg2+ alone. 7. The results are discussed in relation to the interpretation of the kinetic properties of the enzyme and its behaviour in the mitochondrion.

scholarly journals Hepatic Transcriptomics Reveals that Lipogenesis Is a Key Signaling Pathway in Isocitrate Dehydrogenase 2 Deficient Mice

Genes ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 728
Author(s):  
Jeong Hoon Pan ◽  
Jingsi Tang ◽  
Mersady C. Redding ◽  
Kaleigh E. Beane ◽  
Cara L. Conner ◽  
...  
Keyword(s):  
Lipid Metabolism ◽  
Isocitrate Dehydrogenase ◽  
De Novo ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Tca Cycle ◽  
De Novo Lipogenesis ◽  
Oxidative Decarboxylation ◽  
Qpcr Analysis ◽  
Isocitrate Dehydrogenase 2 ◽  
Mice Liver

Mitochondrial nicotinamide adenine dinucleotide phosphate (NADP+)-dependent isocitrate dehydrogenase (IDH2) plays a key role in the intermediary metabolism and energy production via catalysing oxidative decarboxylation of isocitrate to α-ketoglutarate in the tricarboxylic acid (TCA) cycle. Despite studies reporting potential interlinks between IDH2 and various diseases, there is lack of effort to comprehensively characterize signature(s) of IDH2 knockout (IDH2 KO) mice. A total of 6583 transcripts were identified from both wild-type (WT) and IDH2 KO mice liver tissues. Afterwards, 167 differentially expressed genes in the IDH2 KO group were short-listed compared to the WT group based on our criteria. The online bioinformatic analyses indicated that lipid metabolism is the most significantly influenced metabolic process in IDH2 KO mice. Moreover, the TR/RXR activation pathway was predicted as the top canonical pathway significantly affected by IDH2 KO. The key transcripts found in the bioinformatic analyses were validated by qPCR analysis, corresponding to the transcriptomics results. Further, an additional qPCR analysis confirmed that IDH2 KO caused a decrease in hepatic de novo lipogenesis via the activation of the fatty acid β-oxidation process. Our unbiased transcriptomics approach and validation experiments suggested that IDH2 might play a key role in homeostasis of lipid metabolism.

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