Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

The present results suggest that the enzyme modifier citrate and the substrate isocitrate are bound at different sites on yeast NAD-specific isocitrate dehydrogenase and that citrate diminishes the binding of the positive effector 5'-AMP, thereby causing a decreased rate of enzyme catalysis. This interpretation differs from the earlier proposal that citrate can replace isocitrate at an activator site on the enzyme and can cause inhibition by binding at its catalytic site [Atkinson et al. (1965) J. Biol. Chem. 240, 2682]. The present proposal is supported by the following observations: At constant subsaturating levels of isocitrate, NAD+, and Mg2+ without AMP, up to 10 mM citrate was an activator and not an inhibitor. Citrate decreased velocity for AMP-activated enzyme; however, with increasing citrate the specific activity with AMP asymptotically approached but did not decrease below the level of the enzyme maximally activated by citrate in the absence of AMP. When added singly, AMP decreased S0.5 for isocitrate without changing the Hill number (n), whereas citrate lowered n without changing S0.5 for isocitrate. The difference in action of these modifiers indicated that they were bound at separate sites on the enzyme. The binding of citrate appeared to cause a conformational change in the protein that lowered the enzyme's affinity for AMP. This was consistent with the findings that citrate (or the citrate agonist fluorocitrate) (i) resulted in an increase in S0.5 for isocitrate with the AMP-activated enzyme and (ii) decreased binding of the positive effector analogue TNP-AMP as measured by fluorescence change.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Kinetic regulation of yeast NAD-specific isocitrate dehydrogenase by citrate. 200 49

Effects of gossypol on human spermatozoal enzymes were investigated. This compound was found to be a potent inhibitor of the NAD-linked enzymes, glucelaldehyde-3-phosphate dehydrogenase (GA3PDH), lactate dehydrogenase (LDH), malate dehydrogenase (MDH), and isocitrate dehydrogenase (ICDH). MDH was inhibited by gossypol when the reaction was carried out in malate-oxalacetate (direct) or oxalacetate-malate (reverse) directions. The I50 of gossypol for the direct reaction was 2.9 microM, whereas that for the reverse reaction was 1.2 microM. Reciprocal plots due to Lineweaver-Burk showed that MDH is inhibited in a noncompetitive manner with respect to both reactions. LDH was also inhibited by this compound when pyruvate or alpha-ketobutyrate was used as a substrate. Gossypol was a noncompetitive inhibitor for LDH. The I50 of gossypol for LDH were 9.8 microM and 11.3 microM, when using pyruvate and alpha-ketobutyrate, respectively as substrates. The I50 of gossypol for GA3PDH and ICDH were 110 microM and 2.7 microM, respectively.
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PMID:Inhibition kinetics of NAD-linked enzymes by gossypol acetic acid. 207 51

The stimulation of 2-oxoglutarate and NAD(+)-isocitrate dehydrogenase by Ca2+ in mitochondria from normal tissues has been proposed to mediate partially the activation of oxidative energy metabolism elicited by physiological elevations in cytosolic Ca2+. This mode of regulation may also occur in tumor cells in which several aspects of mitochondrial metabolism are known to be altered. This study provides a comparison of the stimulation by submicromolar concentrations of Ca2+ on the rates of ATP-generating (state 3) respiration under physiologically realistic conditions by mitochondria isolated from normal rat liver and from highly malignant rat AS-30D ascites hepatoma cells. The K0.5 for activation of glutamate-dependent state 3 respiration by Ca2+ in the presence of ATP at 37 degrees C was determined to be 0.70 +/- 0.05 (S.E.) microM for hepatoma mitochondria and 0.90 +/- 0.03 microM for rat liver mitochondria. This activation was also reflected by a Ca2(+)-induced shift in the oxidation-reduction state of hepatoma mitochondrial pyridine nucleotides to a more reduced level and Ca2+ stimulation of 14CO2 production from [1-14C]glutamate. Whereas the Ca2+ sensitivity of state 3 respiration by hepatoma mitochondria can be explained by the activation of 2-oxoglutarate and possibly NAD(+)-isocitrate dehydrogenases, the Ca2+ sensitivity of liver mitochondrial respiration appears to be predominantly mediated by activation of electron flow through ubiquinone and Complex III of the electron transport chain, as indicated by the specificity of the effects of Ca2+ on respiration with different oxidizable substrates. Although rat liver and hepatoma mitochondria employ different modes of Ca2(+)-activated ATP generation, these results support the hypothesis that changes in cytosolic Ca2+ play a significant role in the potentiation of energy production in tumor, as well as normal tissue.
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PMID:Submicromolar Ca2+ regulates phosphorylating respiration by normal rat liver and AS-30D hepatoma mitochondria by different mechanisms. 211 59

It was shown that the increase in the activities of transhydrogenase and NAD(+)-dependent isocitrate dehydrogenase after incubation of mitochondria with cAMP is due to the stimulating effect of cAMP on mitochondria, but not to the increased stability of mitochondria to the incubation procedure. Treatment of mitochondria with trypsin prevents the action of cAMP on the both enzymes. The integrity of the inner mitochondrial membrane is necessary for the manifestation of cAMP effect. Pretreatment of mitochondria with the local anesthetic, lidocaine, prevents the activation of NAD(P)(+)-transhydrogenase and NAD(+)-dependent isocitrate dehydrogenase during subsequent incubation of mitochondria with cAMP. It is concluded that the role of the inner mitochondrial membrane consists in the reception of the cAMP signal for the internal compartment of mitochondria, i.e. for mitoplasts. Peripheral protein(s) on the external side of the inner mitochondrial membrane seems to play a role in cAMP reception.
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PMID:[The role of inner membrane in the realization of cAMP-dependent activation of mitochondrial enzymes]. 216 Feb 90

Ten days course of 5'-GMP intramuscular administration at a dose of 25 mg/kg into rats with adrenaline-produced myocarditis led to normalization of NAD content in myocardial tissue which contributed to restoration of NAD-dependent isocitrate dehydrogenase activity. During the 5'-GMP administration content of ATP and creatine phosphate was kept at the same low level as compared with controls, while restoration of glycogen content was retarded in the heart muscle. Activity of lactate dehydrogenase and lactic acid content were not altered. The decrease in content of pyruvic acid detected in response to 5'-GMP administration may occur due to elevated decarboxylation of pyruvate as a result of NAD content increase in heart muscle.
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PMID:[The effect of guanosyl-5'-monophosphate on metabolic processes in rats with experimental myocarditis]. 217 88

Mitochondrial NAD(H)-specific isocitrate dehydrogenase was purified from Saccharomyces cerevisiae for analyses of subunit structure and expression. Two subunits of the enzyme with different molecular weights (39,000 and 40,000) and slightly different isoelectric points were resolved by denaturing electrophoretic techniques. Sequence analysis of the purified subunits showed that the polypeptides have different amino termini. By using an antiserum to the native enzyme prepared in rabbits, subunit-specific immunoglobulin G fractions were obtained by affinity purification, indicating that the subunits are also immunochemically distinct. The levels of NAD(H)-specific isocitrate dehydrogenase activity and immunoreactivity were found to correlate closely with those of a second tricarboxylic acid cycle enzyme, malate dehydrogenase, in yeast cells grown under a variety of conditions. S. cerevisiae mutants with defects in NAD(H)-specific isocitrate dehydrogenase were identified by screening a collection of yeast mutants with acetate-negative growth phenotypes. Immunochemical assays were used to demonstrate that one mutant strain lacks the 40,000-molecular-weight subunit (IDH1) and that a second strain lacks the 39,000-molecular-weight subunit (IDH2). Mitochondria isolated from the IDH1 and IDH2 mutants exhibited a markedly reduced capacity for utilization of either isocitrate or citrate for respiratory O2 consumption. This confirms an essential role for NAD(H)-specific isocitrate dehydrogenase in oxidative functions in the tricarboxylic acid cycle.
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PMID:Subunit structure, expression, and function of NAD(H)-specific isocitrate dehydrogenase in Saccharomyces cerevisiae. 219 51

Patients treated for aneurysmal subarachnoid hemorrhage show, in the long-term follow up, an elevated rate of cognitive disturbances that are mainly related to the impact of the initial bleeding: the neurotoxic effects of blood deposition in subarachnoidal spaces may result in a diffuse encephalopathy, but the intrinsic mechanism and the biochemical correlates are not known. In the present study we have evaluated mitochondrial function after experimental induction of subarachnoid hemorrhage. Mitochondrial function was evaluated in four different rat brain areas (frontal cortex, occipital cortex, hippocampus, and brain stem) after experimental isobaric subarachnoid hemorrhage in rats. Subarachnoid hemorrhage was induced by injecting 0.07 mL of arterial autologous blood into the cisterna magna. Intracranial pressure did not significantly increase. The nonsynaptic mitochondrial fraction was isolated from different rat brain areas, and the maximal rate of enzymatic reactions of some key enzymatic activities related to the Krebs cycle [nicotinamide adenine dinucleotide (oxidized form) (NAD+)-isocitrate dehydrogenase, citrate synthase, and succinate dehydrogenase] and of the electron transfer chain (cytochrome oxidase) were evaluated. The nonsynaptic mitochondrial fraction was utilized also to check parameters related to the mitochondrial respiration: state 3, state 4, uncoupled state, respiratory control ratio, and adenosine 5'-diphosphate/oxygen ratio. The biochemical parameters were measured at 1 and 72 hours after the subarachnoidal injection of blood. Subarachnoid hemorrhage did not affect the mitochondrial enzymatic activities both at 1 and 72 hours, while the mitochondrial enzymatic activities parameters were significantly affected: in particular, a significant decrease of respiratory control ratio in all tested brain areas was demonstrated. The increased mitochondrial vulnerability in the delayed phases could be one of the biochemical correlates of post-hemorrhagic encephalopathy.
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PMID:Experimental isobaric subarachnoid hemorrhage: regional mitochondrial function during the acute and late phase. 221 48

Pig heart NAD-dependent isocitrate dehydrogenase has a subunit structure consisting of alpha 2 beta gamma, with the alpha subunit exhibiting a molecular weight of 39,000 and the beta and gamma each having molecular weights of 41,000. The amino-terminal sequences (33-35 residues) and the cysteinyl peptide sequences have now been determined by using subunits separated by chromatofocusing or isoelectric focusing and electroblotting. Displacement of the N-terminal sequence of the alpha subunit by 11-12 amino acids relative to that of the larger beta and gamma subunits reveals a 17 amino acid region of great similarity in which 10 residues are identical in all three subunits. The complete enzyme has 6.0 free SH groups per average subunit of 40,000 daltons, but yields 15 distinguishable cysteines in isolated tryptic peptides. Six distinct cysteines in sequenced peptides have been located in the alpha subunit. The beta and gamma subunits contain seven and five cysteines, respectively, with tryptic peptides containing three cysteines being common to the beta and gamma subunits. The three subunits appear to be closely related, but beta and gamma are more similar to each other than either is to the alpha subunit. The NAD-specific isocitrate dehydrogenase from pig heart has been shown to have 2 binding sites/enzyme tetramer for isocitrate, manganous ion, NAD+, and the allosteric activator ADP [Colman, R. F. (1983) Pept. Protein Rev. 1, 41-69]. It is proposed that the catalytically active tetrameric enzyme is organized as a dimer of dimers in which the alpha beta and alpha gamma dimers are nonidentical but functionally similar.
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PMID:Subunit location and sequences of the cysteinyl peptides of pig heart NAD-dependent isocitrate dehydrogenase. 225 88

NAD(+)-dependent isocitrate dehydrogenase from pig heart is an allosteric enzyme that is activated by ADP and is inhibited by NADPH in the presence of NADH. Transferred nuclear Overhauser effect measurements, made at a range of times to ensure that observed effects are due to direct dipole-dipole transfer and not to spin diffusion, were used to determine the conformations of pyridine nucleotide coenzymes and of the allosteric effector ADP. For NAD+, significant effects were observed on the N2 proton (on the nicotinamide ring) when the N1' proton (on the nicotinamide ribose) was saturated and on the N6 proton when the N2' proton was saturated, indicating that the conformation of the nicotinamide-ribose moiety is anti. The anti conformation is expected because of the stereospecificity of NAD(+)-dependent isocitrate dehydrogenase and is the same as for NADP(+)-dependent isocitrate dehydrogenase. For the adenosine moiety of NAD+, the predominant nuclear Overhauser effect on the A8 proton is found when the A2' proton is saturated. This result implies that the adenine-ribose bond is anti with respect to the ribose. Previous kinetic and binding studies of ADP activation have shown an influence of divalent metal ions. The conformation of bound ADP, in the presence of Mg2+ and/or Ca2+, is found to be anti about the adenine-ribose bond. The 3'H-8H distance increases when Ca2+ is added to the Mg-ADP-enzyme complex. Changes in the 4'H-1'H distance upon addition of isocitrate are indicative of interactions between the ADP activator site and the isocitrate site.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Conformations of the coenzymes and the allosteric activator, ADP, bound to NAD(+)-dependent isocitrate dehydrogenase from pig heart. 237 74

In extracts of rat heart mitochondria, Sr2+ mimicked the activatory effects of Ca2+ on the Ca2(+)-sensitive intramitochondrial enzymes, pyruvate dehydrogenase phosphate phosphatase, isocitrate dehydrogenase (NAD+), and 2-oxoglutarate dehydrogenase, but at about tenfold higher concentrations (effective range approximately 1-100 muM) in each case. Ba2+ had no effect on extracted phosphatase, but did mimic the effect of Ca2+ on the other two enzymes with effective concentration ranges similar to those of Sr2+; as with Ca2+ and Sr2+, effective Ba2+ ranges were slightly (2-3-fold) raised by increases in ATP/ADP. In intact uncoupled rat heart mitochondria, the effects of Sr2+ and Ba2+ on the pyruvate and 2-oxoglutarate dehydrogenases were essentially similar to their effects in extracts. In fully coupled rat heart or liver mitochondria, the effective concentration ranges of extramitochondrial Sr2+, leading to activation of the matrix enzymes, were always approximately tenfold higher than those for Ca2+ under all conditions. Ba2+ did not affect pyruvate dehydrogenase in coupled mitochondria, but was shown to activate 2-oxoglutarate dehydrogenase in heart or liver mitochondria, and also isocitrate dehydrogenase (NAD+) in the latter; effective concentration ranges for extramitochondrial Ba2+ were approximately 100-fold greater than those for Ca2+, and like those for Ca2+ and Sr2+, were affected markedly by Mg2+ and spermine (which inhibit and promote mitochondrial Ca2+ uptake, respectively) but, in contrast to Ca2+ and Sr2+, they were hardly affected at all by Na+ (which promotes mitochondrial Ca2+ egress). Ba2+ effects were also blocked by ruthenium red (an inhibitor of mitochondrial Ca2+ uptake), but not so effectively as its blockage of the effects of Sr2+ and Ca2+. Ba2+ and Sr2+ both mimicked the inhibitory effects of extramitochondrial Ca2+ on the Na+/Ca2+ exchanger, but only Sr2+ could mimic Ca2+ in exchanging for internal Ca2+ by this mechanism. Both Sr2+ and Ba2+ changed the fluorescent properties of fura-2 or indo-1 in a similar manner to Ca2+, but with higher kd values. In fura-2-loaded rat heart mitochondria, increases in matrix Sr2+ and Ba2+ and the effects of the transport effectors could be readily demonstrated.
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PMID:The use of the Ca2(+)-sensitive intramitochondrial dehydrogenases and entrapped fura-2 to study Sr2+ and Ba2+ transport across the inner membrane of mammalian mitochondria. 240 Dec 95


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