Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.1.1.41 (isocitrate dehydrogenase)
3,101 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The reversal of the mitochondrial isocitrate dehydrogenase reaction was investigated in rat livers perfused with [U-13C5]glutamate or [U-13C5]glutamine. The mass isotopomer distribution of citric acid cycle intermediates extracted from the livers was determined by gas chromatography-mass spectrometry. Citrate was enriched in an isotopomer containing five 13C. The formation of this isotopomer can only be explained by the reversal of the isocitrate dehydrogenase reaction. Calculation of kinetic parameters from the mass isotopomer data reveals a rapid interconversion of isocitrate and alpha-ketoglutarate. This interconversion results in an isotopic exchange between carbon 6 of citrate and mitochondrial CO2 that can affect the calculation of citric acid cycle kinetic parameters. Thus, the reversal of the isocitrate dehydrogenase reaction should be included in isotope labeling models of the citric acid cycle.
...
PMID:Reversibility of the mitochondrial isocitrate dehydrogenase reaction in the perfused rat liver. Evidence from isotopomer analysis of citric acid cycle intermediates. 796 26

A new enzymatic method for assaying iron in serum samples, suitable for automated analyzers, is reported. Three reagent mixtures are used: dilution buffer (pH 3.0; ascorbate), reagent 1 (pH 6.7; apoaconitase), and reagent 2 (pH 7.7; citrate, magnesium, and isocitrate dehydrogenase). Sera are diluted with dilution buffer. Fe3+ is liberated from transferrin in sera under acidic conditions, and then reduced by ascorbate. Reagent 1 is added to diluted specimens, and apoaconitase is reactivated by Fe2+ at neutral pH. The resulting solutions are mixed with reagent 2, so that holoaconitase hydrolyzes citrate to isocitrate and the isocitrate and NADP+ are converted to 2-oxoglutarate, NADPH, and CO2. Serum iron is determined linearly up to 70 mumol/L, with within-run CVs < or = 2.4% and day-to-day CVs < or = 2.9%. This method (y) gives results correlating with those of a Reference Method (x) proposed by the International Committee for Standardization in Haematology: y = 0.98x + 0.38 mumol/L (n = 72, r = 0.996, Sylx = 0.63 mumol/L). The mean (+/- SD) serum iron concentrations measured by our method were 18.5 +/- 5.4 and 15.2 +/- 6.0 mumol/L for 63 males and 166 females, respectively.
...
PMID:New enzymatic assay of iron in serum. 817 49

Oxalobacter formigenes is the only well-documented oxalate-degrading bacterium isolated from the gastrointestinal tract of animals. The production of ATP by Oxalobacter formigenes is centered around oxalate metabolism and oxalate is required for growth. A small amount of acetate (0.5 mM) is also required. Oxalate is decarboxylated to formate plus CO2 in nearly equimolar amounts. Experiments were conducted to determine which potential carbon sources (oxalate, acetate, formate, CO2) were assimilated by Oxalobacter formigenes and which metabolic pathways were operative in carbon assimilation. Measurements of the specific activities of total cell carbon after growth with different 14C-labeled precursors indicated that at least 54% of the total cell carbon was derived from oxalate and at least 7% was derived from acetate. Carbonate was also assimilated, but formate was not a significant source of cell carbon. Labeling patterns in amino acids from cells grown in [14C]oxalate or 14CO3 were different; however, in both cases 14C was widely distributed into most cellular amino acids. Carbon from [14C]acetate was less widely distributed and detected mainly in those amino acids known to be derived from alpha-ketoglutarate, oxaloacetate, and pyruvate. Cell-free extracts contained citrate synthase, isocitrate dehydrogenase, and malate dehydrogenase activities. The labeling observed in amino acids derived from acetate is in agreement with the function of these enzymes in biosynthesis and indicates that the majority of acetate carbon entered into amino acid biosynthesis via well-known pathways.
...
PMID:Assimilation of oxalate, acetate, and CO2 by Oxalobacter formigenes. 894 83

A stoichiometric model describing the anaerobic metabolism of Saccharomyces cerevisiae during growth on a defined medium was derived. The model was used to calculate intracellular fluxes based on measurements of the uptake of substrates from the medium, the secretion of products from the cells, and of the rate of biomass formation. Furthermore, measurements of the biomass composition and of the activity of key enzymes were used in the calculations. The stoichiometric network consists of 37 pathway reactions involving 43 compounds of which 13 were measured (acetate, CO2, ethanol, glucose, glycerol, NH4+, pyruvate, succinate, carbohydrates, DNA, lipids, proteins and RNA). The model was used to calculate the production rates of malate and fumarate and the ethanol measurement was used to validate the model. All rate measurements were performed on glucose-limited continuous cultures in a high-performance bioreactor. Carbon balances closed within 98%. The calculations comprised flux distributions at specific growth rates of 0.10 and 0.30 h-1. The fluxes through reactions located around important branch points of the metabolism were compared, i.e. the split between the pentose phosphate and the Embden-Meyerhoff-Parnas pathways. Also the model was used to show the probable existence of a redox shunt across the inner mitochondrial membrane consisting of the reactions catalysed by the mitochondrial and the cytosolic alcohol dehydrogenase. Finally it was concluded that cytosolic isocitrate dehydrogenase is probably not present during growth on glucose. The importance of basing the flux analysis on accurate measurements was demonstrated through a sensitivity analysis. It was found that the accuracy of the measurements of CO2, ethanol, glucose, glycerol and protein was critical for the correct calculation of the flux distribution.
...
PMID:Flux distributions in anaerobic, glucose-limited continuous cultures of Saccharomyces cerevisiae. 902 95

Growth of Corynebacterium glutamicum on fructose was significantly less than that obtained on glucose, despite similar rates of substrate uptake. This was in part due to the production of overflow metabolites (dihydroxyacetone and lactate) but also to the increased production of CO2 during growth on fructose. These differences in carbon-metabolite accumulation are indicative of a different pattern of carbon-flux distribution through the central metabolic pathways. Growth on glucose has been previously shown to involve a high flux (> 50% of total glucose consumption) via the pentose pathway to generate anabolic reducing equivalents. NMR analysis of carbon-isotope distribution patterns of the glutamate pool after growth on 1-13C- or 6-13C-enriched fructose indicates that the contribution of the pentose pathway is significantly diminished during exponential growth on fructose with glycolysis being the predominant pathway (80% of total fructose consumption). The increased flux through glycolysis during growth on fructose is associated with an increased NADH/NAD+ ratio susceptible to inhibit both glyceraldehyde-3-phosphate dehydrogenase and pyruvate dehydrogenase, and provoking the overflow of metabolites derived from the substrates of these two enzymes. The biomass yield observed experimentally is higher than can be estimated from the apparent quantity of NADPH associated with the pentose pathway and the flux through isocitrate dehydrogenase, suggesting an additional reaction yielding NADPH. This may involve a modified tricarboxylic acid cycle involving malic enzyme, expressed to significantly higher levels during growth on fructose than on glucose, and a pyruvate carboxylating anaplerotic enzyme.
...
PMID:Carbon-flux distribution in the central metabolic pathways of Corynebacterium glutamicum during growth on fructose. 965

The structure of a rate-limited product complex formed during a single initial round of turnover by isocitrate dehydrogenase has been determined. Photolytic liberation of either caged substrate or caged cofactor and Laue X-ray data collection were used to visualize the complex, which has a minimum half-life of approximately 10 milliseconds. The experiment was conducted with three different photoreactive compounds, each possessing a unique mechanism leading to the formation of the enzyme-substrate (ES) complex. Photoreaction efficiency and subsequent substrate affinities and binding rates in the crystal are critical parameters for these experiments. The structure suggests that CO2 dissociation is a rapid event that may help drive product formation, and that small conformational changes may contribute to slow product release.
...
PMID:Millisecond Laue structures of an enzyme-product complex using photocaged substrate analogs. 978 49

Variations of intracellular concentrations of isocitrate and NADP+ were measured throughout all growth phases of the marine bacterium Pseudomonas nautica. The intracellular isocitrate concentration tracked the intracellular protein concentration throughout all phases of growth. It rapidly increased in early exponential phase to a maximum and fell to nearly zero in parallel with pyruvate exhaustion in the culture medium. The intracellular NADP+ and protein concentrations increased in parallel during the exponential phase but were poorly correlated. Even after carbon exhaustion, the intracellular NADP+ concentration stayed high, as did protein levels. The results demonstrated that the intracellular isocitrate concentration, but not the intracellular NADP+ concentration, was affected by the carbon availability in the culture. They also suggest that, because of its variability, isocitrate, but not NADP+, plays the larger role in the control of the respiratory CO2 production rate (RCO2). From initial rate studies, bisubstrate Michaelis constants and the dissociation constant were determined for NADP+-specific isocitrate dehydrogenase (IDH) from P. nautica. These studies support the hypothesis that the mechanism of IDH's activity involves the ordered addition of the substrates, D-isocitrate and NADP+. Furthermore, the results support the use of a bisubstrate enzyme kinetic equation to model RCO2 in P. nautica.
...
PMID:NADP-Isocitrate dehydrogenase from Pseudomonas nautica: kinetic constant determination and carbon limitation effects on the pool of intracellular substrates. 983 89

The content of free sugars and the activities of enzymes involved in carbon metabolism-sucrose synthase, acid and alkaline invertase, phosphoenol pyruvate carboxylase, malic enzyme and isocitrate dehydrogenase were determined during seed development in mungbean pods. A decrease in carbohydrate content of pod wall from 10 to 25 days after flowering (DAF) and a concomitant increase in the seed till 20 DAF was observed. Sucrose remained the dominant soluble sugar in the pod wall and seed. In the branch of inflorescence and pod wall, the activities of sucrose metabolizing enzymes, viz. acid and alkaline invertase, sucrose synthase (synthesis and cleavage) and sucrose phosphate synthase were higher at 5-10 DAF, whereas in seed the maximum activities of these enzymes were observed at the time of maximum seed filling stage (10-20 DAF). High activities of sucrose synthase at the time of rapid seed filling can be correlated to its sink strength. Higher activities of phosphoenol pyruvate carboxylase in the branch of inflorescence and pod wall than in seed may indicate the involvement of the fruiting structure for recapturing respired CO2. High activities of isocitrate dehydrogenase and malic enzyme in the seed at the time of rapid seed filling could provide NADPH and carbon skeletons required for the synthesis of various seed reserves.
...
PMID:Ontogenic changes in enzymes of carbon metabolism in relation to carbohydrate status in developing mungbean reproductive structures. 1072 78

The stereospecificity of the enzyme isocitrate dehydrogenase was examined by steady-state kinetics and x-ray crystallography. The enzyme has the intriguing property that the apoenzyme in the absence of divalent metal showed a selectivity for the inactive l-enantiomer of the substrate isocitrate, whereas the enzyme containing magnesium showed selectivity for the physiologically active d-enantiomer. The hydrogen atom on the C2 carbon that is transferred during the reaction was, in both the d- and l-isocitrate complexes, in an orientation very close to that expected for delivery of a hydride ion to the cosubstrate NADP+. The beta-carboxylate that is eliminated as a CO2 molecule during the reaction occupied the same site on the protein in both the d- and l-isocitrate complexes. In addition, the C3 carbon was in the same protein site in both the d- and l-enantiomers. Only the fourth group, the OH atom, was in a very different position in the apo enzyme and in the metal-containing complexes. A four-location model is necessary to explain the enantiomeric specificity of IDH in contrast to the conventional three-point attachment model. The thermodynamic and kinetic ramifications of this model are explored.
...
PMID:Sites of binding and orientation in a four-location model for protein stereospecificity. 1090 79

The metabolic cross-talk associated with re-assimilation of photorespiratory NH4+ was analysed in transformed tobacco (Nicotiana tabacum L.) plants with low activities of ferredoxin-dependent glutamine-alpha-ketoglutarate aminotransferase (Fd-GOGAT; EC 1.4.7.1). Amounts of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) protein and Rubisco transcripts were similar in all lines whether photorespiration rates were low (4,000 microl l(-1) CO2) or high (air). Leaf sucrose, hexose and starch contents were similar in all lines. In contrast, there was evidence that anaplerotic carbon flow was stimulated in the transformed lines with less than 60% Fd-GOGAT, since phospho enolpyruvate carboxylase (PEPc) activity and (PEPc) protein were increased. A strong positive correlation between leaf PEPc activity and glutamine accumulation was observed, suggesting that the increase in PEPc was related to the accumulation of glutamine. A modest stimulation of total NADP-isocitrate dehydrogenase (ICDH; EC 1.1.1.42) activity was also observed in the transformed lines with less than 60% Fd-GOGAT. This was accompanied by increases in both the cytosolic ICDH and mitochondrial NAD-isocitrate dehydrogenases (IDH; EC 1.1.1.41). IDH protein was also increased in the transformed plants with low Fd-GOGAT, suggesting that both IDH and ICDH are involved in the production of carbon skeletons (and ultimately alpha-ketoglutarate) necessary for the re-assimilation of NH4+. In contrast, PEPc, ICDH and IDH transcripts were similar in all lines. The aminating (but not the de-aminating) activity of NAD(H)-glutamate dehydrogenase (NAD(H)-GDH; EC 1.4.1.2) was greatly increased in plants with less than 60% of Fd-GOGAT after transfer to air. The data confirm that NH4+ or glutamine are involved in signalling, leading to modified gene expression and enzyme activity required for enhanced production of the C skeletons, to accommodate increases in the assimilation of photorespiratory NH4+. In addition, we provide the first demonstration of a compensatory role for NAD(H)-GDH in stabilising the leaf glutamic acid pool when Fd-GOGAT becomes limiting.
...
PMID:Photorespiration-dependent increases in phospho enolpyruvate carboxylase, isocitrate dehydrogenase and glutamate dehydrogenase in transformed tobacco plants deficient in ferredoxin-dependent glutamine-alpha-ketoglutarate aminotransferase. 1194 64


<< Previous 1 2 3 4 5 Next >>

---