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

Three important dehydrogenases in the mitochondria of mammalian tissues are activated by Ca2+ ions: these are pyruvate dehydrogenase, NAD-isocitrate dehydrogenase, and oxoglutarate dehydrogenase. Evidence is summarized that when hormones and other extracellular stimuli increase the cytoplasmic concentration of Ca2+ in rat hearts and livers that this results in a parallel rise in the intramitochondrial concentration of Ca2+. In this way, pyruvate oxidation and citric acid cycle flux are stimulated and there is an increase in NADH supply for the respiratory chain under conditions where there is an enhanced demand for ATP.
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PMID:Effects of Ca2+ on the activities of the calcium-sensitive dehydrogenases within the mitochondria of mammalian tissues. 246 81

The relationship of extramitochondrial Ca2+ to intramitochondrial Ca2+ and the influence of intramitochondrial free Ca2+ concentrations on various steps of the citric acid cycle were evaluated. Ca2+ was measured using the Ca2+ sensitive fluorescent dye fura-2 trapped inside the rat heart mitochondria. The rate of utilization of specific substrates and the rate of accumulation of citric acid cycle intermediates were measured at matrix free Ca2+ ranging from 0 to 1.2 microM. A change in matrix free Ca2+ from 0 to 0.3 microM caused a 135% increase in ADP stimulated oxidation of 0.6 mM alpha-ketoglutarate (K0.5 = 0.15 microM). In the absence of ADP and the presence of 0.6 mM alpha-ketoglutarate, Ca2+ (0.3 microM) increased NAD(H) reduction from 0 to 40%. On the other hand, when pyruvate (10 microM to 5 mM) was substrate, pyruvate dehydrogenase flux was insensitive to Ca2+ and isocitrate dehydrogenase was sensitive to Ca2+ only in the presence of added ADP. In separate experiments pyruvate dehydrogenase activation (dephosphorylation) was measured. Under the conditions of the present study, pyruvate dehydrogenase was found to be almost 100% activated at all levels of Ca2+, thus explaining the Ca2+ insensitivity of the flux measurements. However, if the mitochondria were incubated in the absence of pyruvate, with excess alpha-ketoglutarate and excess ATP, the pyruvate dehydrogenase complex was only 20% active in the absence of added Ca2+ and activity increased to 100% at 2 microM Ca2+. Activation by Ca2+ required more Ca2+ (K0.5 = 1 microM) than for alpha-ketoglutarate dehydrogenase. The data suggest that in heart mitochondria alpha-ketoglutarate dehydrogenase may be a more physiologically relevant target of Ca2+ action than pyruvate dehydrogenase.
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PMID:Regulation of citric acid cycle by calcium. 250 1

The coupling free energy between an allosteric ligand and a substrate, delta Gax, is an explicit measure of the nature as well as the magnitude of impact that an allosteric ligand has on the binding of the substrate ligand to the enzyme, with positive values indicating inhibition and negative values indicating activation. By measuring the variation with temperature of the coupling free energy between the allosteric ligand and the substrate, it is possible to determine the enthalpic and entropic components that give rise to the coupling free energy. We have performed this analysis on two different K-type allosteric systems: the allosteric inhibition of rat liver phosphofructokinase by MgATP, and the allosteric activation of beef heart NAD+-dependent isocitrate dehydrogenase by ADP. In both cases the coupling free energy arises as the net result of opposing enthalpic and entropic components, with the coupling enthalpy (delta Hax) favoring activation and the coupling entropy (delta Sax) favoring inhibition. For phosphofructokinase at 25 degrees C, the absolute value of T delta Sax is greater than the absolute value of delta Hax, and net inhibition of rat liver phosphofructokinase by MgATP is realized. For isocitrate dehydrogenase, delta Hax dominates; however, the net activation is substantially mitigated by the magnitude of T delta Sax. Hence, the coupling entropy plays an important role in establishing both the nature and magnitude of the allosteric response. We hypothesize that the negative coupling entropy arises from the particular constraint placed upon the internal dynamical properties of the enzyme by the simultaneous binding of both allosteric and substrate ligands.
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PMID:Role of coupling entropy in establishing the nature and magnitude of allosteric response. 252 36

We have previously reported that rats fed on the Steenbock and Black's rickets-inducing diet (deficient in vitamin D and with an altered Ca/P ratio) show metabolic modifications in kidney and intestinal mucosa. We have therefore decided to investigate if also in liver, seat of vitamin D hydroxylation, changes in the metabolic pattern occur. An increase of mitochondrial NAD+-dependent isocitrate dehydrogenase and a decrease of citrate and ATP content was demonstrated in liver of rachitic rats, together with changes in ATP-citrate lyase and glucose-6-phosphate dehydrogenase activity. The inhibitory effect of ATP on liver mitochondria NAD+-dependent isocitrate dehydrogenase was also studied.
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PMID:[Influence of a rachitogenic regime on hepatic metabolism in the rat]. 253 Oct 20

The substrate affinity label 3-bromo-2-ketoglutarate (BrKG) reacts covalently with pig heart NAD+-specific isocitrate dehydrogenase with complete inactivation and incorporation of about 0.8 mol of reagent/mol of average enzyme subunit [Bednar, R.A., Hartman, F.C., & Colman, R.F. (1982) Biochemistry 21, 3681-3689]. Protection against inactivation is provided by isocitrate and Mn2+. We have now identified a critical modified peptide by comparison of the peptides labeled by BrKG at pH 6.1 in the absence and presence of isocitrate and Mn2+. Modified enzyme, isolated from unreacted BrKG, was incubated with [3H]NaBH4 to reduce the keto group of protein-bound 2-ketoglutarate and thereby introduce a radioactive tracer into the modified amino acid. Following carboxymethylation and digestion with trypsin, the specific modified peptide was isolated by reverse-phase HPLC, first in 0.1% trifluoroacetic acid with a gradient in acetonitrile and then in 20 mM ammonium acetate, pH 5.8, with an acetonitrile gradient. Gas-phase sequencing gave the modified peptide: Ser-Ala-X-Val-Pro-Val-Asp-Phe-Glu-Glu-Val-Val-Val-Ser-Ser-Asn-Ala-Asp-Gl u-Glu- Asp-Ile-Arg. The corresponding tryptic peptide that was isolated from unmodified enzyme yielded the same sequence except for (carboxymethyl)cysteine at position 3, suggesting that cysteine is the target of 3-bromo-2-ketoglutarate. Pig heart NAD+-dependent isocitrate dehydrogenase is composed of three distinct subunits (alpha, beta, and gamma) that can be separated by chromatofocusing in urea and identified by analytical gel isoelectric focusing. The peptide modified by 3-bromo-2-ketoglutarate, which is in or near the substrate site, is derived only from the separated gamma subunit.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cysteinyl peptide labeled by 3-bromo-2-ketoglutarate in the active site of pig heart NAD+-dependent isocitrate dehydrogenase. 260 93

The early stages of insulin-dependent diabetes mellitus are characterized by a selective inability to secrete insulin in response to glucose, coupled to a better response to nonnutrient secretagogues. The deficient glucose response may be a result of the autoimmune process directed toward the beta-cells. Interleukin-1 (IL-1) has been suggested to be one possible mediator of immunological damage of the beta-cells. In the present study we characterized the sensitivity of beta-cells to different secretagogues after human recombinant IL-1 beta (rIL-1 beta) exposure. Furthermore, experiments were performed to clarify the biochemical mechanisms behind the defective insulin response observed in these islets. Rat pancreatic islets were isolated and kept in tissue culture (medium RPMI-1640 plus 10% calf serum) for 5 days. The islets were subsequently exposed to 60 pM human recombinant IL-1 beta during 48 h in the same culture conditions as above and examined immediately after IL-1 exposure. The rIL-1 beta-treated islets showed a marked reduction of glucose-stimulated insulin release. Stimulation with arginine plus different glucose concentrations, and leucine plus glutamine partially counteracted the rIL-1 beta-induced reduction of insulin release. The activities of the glycolytic enzymes hexokinase, glucokinase, and glyceraldehyde 3-phosphate dehydrogenase, were similar in control and IL-1-exposed islets. Treatment with IL-1 also did not impair the activities of NADH+- and NADPH+-dependent glutamate dehydrogenase, glutamate-aspartate transaminase, glutamate-alanine transaminase, citrate synthase, and NAD+-linked isocitrate dehydrogenase. The oxidation of D-[6-14C]glucose and L-[U-14C]leucine were decreased by 50% in IL-1-treated islets. Furthermore, there was a significant decrease in the ratios of [2-14C]pyruvate oxidation/[1-14C]pyruvate decarboxylation and L-[U-14C]leucine oxidation/L-[1-14C]leucine decarboxylation, indicating that IL-1 decreases the proportion of generated acetyl-coenzyme-A residues undergoing oxidation. However, in the presence of IL-1 there was a significant increase in L-[U-14C]glutamate oxidation. These combined observations suggest that exposure to IL-1 induces a preferential decrease in glucose-mediated insulin release and mitochondrial glucose metabolism. This mitochondrial dysfunction seems to reflect an impairment in proximal steps of the Krebs cycle. It is conceivable that the IL-1-induced suppression and shift in islet metabolism can be an explanation for the beta-cell insensitivity to glucose observed in the early phases of human and experimental insulin-dependent diabetes mellitus.
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PMID:Differential sensitivity to beta-cell secretagogues in cultured rat pancreatic islets exposed to human interleukin-1 beta. 266 6

The morphologic changes in sodium-maleate-induced acute renal injury in the rat were quantified by a stereologic analysis. The major changes were confined to an increase in endocytic vacuoles and a decrease in mitochondrial inner membrane surface area. These results were found to be linked to significantly increased urinary activities of the cytosolic of the cytosolic enzymes fructose-1,6-bisphosphatase (FBP) and lactate dehydrogenase, the lysosomal enzyme N-acetyl-beta-glucosaminidase (NAG) and the NAD-dependent mitochondrial isocitrate dehydrogenase (ICDH). The highest increase was found for NAG, followed by FBP and ICDH.
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PMID:Quantitative morphologic changes in nephron structures and urinary enzyme activity pattern in sodium-maleate-induced renal injury. 272 85

The nucleotide affinity label 2-(4-bromo-2,3-dioxobutylthio)adenosine 5'-diphosphate (2-BDB-TADP) reacts covalently with pig heart NAD+-dependent isocitrate dehydrogenase with a limiting value of 75% inactivation and loss of ADP activation concomitant with incorporation of about 1 mol of reagent/mol of average enzyme subunit (Huang, Y.-C., Bailey, J. M., and Colman, R. F. (1986) J. Biol. Chem. 251, 14100-14107). Complete protection against the functional changes is provided by ADP + Mn2+, and reagent incorporation is decreased to about 0.5 mol/mol of average enzyme subunit. We have now identified the critical modified peptide by comparison of the peptides labeled by 2-BDB-TADP at pH 6.8 in the absence and presence of ADP + Mn2+. After removal of excess reagent, modified enzyme was treated with [3H]NaBH4 to reduce the keto groups of the reagent and introduce a radioactive tracer into the reagent which is covalently linked to the protein. Following carboxymethylation and digestion with trypsin, the specific modified peptide was isolated using two successive high performance liquid chromatography steps: 1) 0.1% trifluoroacetic acid with an acetonitrile gradient; and 2) 20 mM ammonium acetate, pH 5.8, with an acetonitrile gradient. Gas phase sequencing gave the modified peptide Leu-Gly-Asp-Gly-Leu-Phe-Leu-Gln in which aspartic acid is the target of 2-BDB-TADP. Isolation of the corresponding tryptic peptide from unmodified enzyme yielded the sequence Leu-Gly-Asp-Gly-Leu-Phe-Leu-Gln-CmCys-CmCys-Lys. Isocitrate dehydrogenase is composed of three distinct subunits (alpha, beta, and gamma), separable by chromatofocusing in urea and identified by analytical gel isoelectric focusing. The evidence indicates that the specific peptide labeled by 2-BDB-TADP, which is at or near the ADP site, can be derived from the gamma subunit.
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PMID:Aspartyl peptide labeled by 2-(4-bromo-2,3-dioxobutylthio)adenosine 5'-diphosphate in the allosteric ADP site of pig heart NAD+-dependent isocitrate dehydrogenase. 274 37

1. The activities of phosphoenolpyruvate carboxykinase, malic enzyme, NAD+ and NADP+ isocitrate isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and pyruvate kinase were assayed in homogenate of camel hump and sheep tail tissues. 2. In addition the levels of glucose, cholesterol, total protein and total lipids in these tissues were measured. 3. Results obtained were utilized to compare the state of metabolism of adipose tissue of camel hump to that of sheep tail, and to shed some light on possible contribution of these tissues toward blood glucose level.
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PMID:A comparative study of enzyme profile of camel (Camelus dromedarius) hump and sheep (Ovis aries) tail tissues. 280 43

Early iron deficiency in rat does not affect the weight or the protein, DNA, and RNA content but results in a slight reduction in gamma-aminobutyric acid (GABA) (13%, p less than 0.01) and glutamic acid (20%, p less than 0.001) content of the brain. The activities of the two GABA shunt enzymes, glutamate dehydrogenase and GABA-transaminase, and of the NAD+-linked isocitrate dehydrogenase (ICDH) were inhibited whereas the glutamic acid decarboxylase, mitochondrial NADP+-linked ICDH, and succinic dehydrogenase activities remained unaltered in brain. On rehabilitation with the iron-supplemented diet for 1 week, these decreased enzyme activities in brain attained the corresponding control values. However, the hepatic nonheme iron content increased to about 80% of the control, after rehabilitation for 2 weeks. A prolonged iron deficiency resulting in decreased levels of glutamate and GABA may lead to endocrinological, neurological, and behavioral alterations.
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PMID:Effect of early iron deficiency in rat on the gamma-aminobutyric acid shunt in brain. 287 Nov 28


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