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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)

Activity of pyruvate dehydrogenase (PDG), isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase and malate dehydrogenase was found in the extracts of the cells of Bac. polymyxa 153, an organism producing polymyxin B. Dependence of the activity of the above enzymes on the carbon source in the medium, aeration conditions, strain features and culture age was shown. A low level of polymyxin B biosynthesis was observed at high activity of PDG and dehydrogenases of the tricarbonic acid cycle. Increased antibiotic production was recorded against the background of decreases values of the above enzyme activities.
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PMID:[Polymyxin B biosynthesis and tricarboxylic acid cycle enzymatic activity]. 21 Jul 9

Subepicardial and subendocardial arteries and arterioles in both the left and right normal canine ventricle were examined histochemically to determine their metabolic profiles. Aerobic metabolic capacity was assessed by determining the reactivities of the enzymes cytochrome oxidase, succinate dehydrogenase and NAD-isocitrate dehydrogenase. Glucose-6-phosphate dehydrogenase was examined to assess activity of the hexose-monophosphate-shunt. The substrate glycogen was determined as an evaluation of anaerobic metabolic capacity, while the amounts of deoxyribonucleic and ribonucleic acid were assessed as an indication of protein synthesis. Results of the present investigation indicate that despite known hemodynamic differences, the metabolic profile of the coronary vasculature is similar in all regions of ventricular myocardium. Reactivities of the enzymes succinate and NAD-isocitrate dehydrogenase and cytochrome oxidase are greater in smooth muscle of arterioles than in arteries. This suggests that arteriolar smooth muscle has a higher capacity for aerobic metabolism than does arterial smooth muscle. The greater reactivity of glycogen in arterial, than in arteriolar smooth muscle, suggests that arterial muscle is more adapted for anaerobic metabolism. Deoxyribonucleic and ribonucleic acids demonstrate a low reactivity in both arteries and arterioles from all regions of ventricular myocardium which conforms to the opinion that under normal conditions, coronary vasculature is quite stable with little cell proliferation. Glucose-6-phosphate dehydrogenase shows little reactivity in all myocardial vessels with implies a low capacity for nucleic acid and protein synthesis.
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PMID:A histochemical study of the microvasculature in the left and right cardiac ventricles of the dog. 21 88

Heterogeneity in the subunits of nicotinamide adenine dinucleotide dependent isocitrate dehydrogenase from beef heart mitochondria was investigated using one- and two-dimensional electrophoretic analyses in polyacrylamide gels. Electrophoresis under nondenaturing conditions, at several values of pH and gel concentration, followed by second-dimension electrophoresis in the presence of sodium dodecyl sulfate showed that the active enzyme contains four different subunits. The details of these two-dimensional patterns, reelectrophoresis of the active enzyme band under nondenaturing conditions, together with additional evidence indicate that under certain nondenaturing conditions the enzyme exists partially dissociated into its subunits. The molecular weights of the four subunits, determined from electrophoretic mobilities obtained in the presence of sodium dodecyl sulfate, were different, varying between 39 000 and 41 300. Tryptic peptide maps of the subunits are substantially different.
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PMID:Nicotinamide adenine dinucleotide dependent isocitrate dehydrogenase from beef heart: subunit heterogeneity and enzyme dissociation. 21 97

The effects of Ca2+ on the activity of isocitrate dehydrogenase (NAD+) in extracts of rat heart mitochondria were explored in the presence of MgCl2 by using EGTA buffers. In the absence of ADP, Ca2+ (about 30 micrometer) resulted in a slight increase in apparent Km for threo-Ds-isocitrate; in the presence of ADP, Ca2+ (about 25 micrometer) greatly lowered the apparent Km for threo-Ds-isocitrate from 227 micrometer to 53 micrometer without changing the maximum velocity. At 100 micrometer-threo-Ds-isocitrate and 1 mM-ADP, there was an 8-fold activation by Ca2+, with a Km for Ca2+ of 1.2 micrometer. This activation was also observed with Sr2+ (Km 3.1 micrometer), but not with Mn2+ (at concentrations below 2.5 micrometer). Similar effects of Ca2+ were also observed on isocitrate dehydrogenase (NAD+) activity in extracts of mitochondria from liver, kidney, brown adipose tissue and white adipose tissue of the rat. The possible regulatory role of changes in the intramitochondrial concentration of Ca2+ is discussed.
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PMID:Calcium ions and the regulation of NAD+-linked isocitrate dehydrogenase from the mitochondria of rat heart and other tissues. 21 57

A realistic metabolic model of the tricarboxylic acid cycle in the perfused rat heart was constructed to help explain the sequence of biochemical events regulating the metabolism of exogenous pyruvate following a large increase in work load. The unchelated Mg2+ level was the most important controlling factor. The resulting mixture of chelated and unchelated nucleotides and tribasic acids effected coordinated control of citrate synthase, aconitase, isocitrate dehydrogenase, succinyl CoA synthetase, fumarase, and nucleoside diphosphokinase, because Mg2+-chelates are generally substrates whereas unchelated species are inhibitors. Succinate dehydrogenase is largely controlled by the ubiquinone redox potential. The fluxes through alpha-ketoglutarate and malate dehydrogenases are largely dependent on thepyridine nucleotide redox potential, but the succinyl CoA-to-CoASH ratio strongly affects the former enzyme as well. The model predicts an accumulation of succinate during the transition to higher work output.
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PMID:Computer simulation of metabolism in pyruvate-perfused rat heart. II. Krebs cycle. 22 18

Neurospora crassa nicotinamide adenine dinucleotide specific isocitrate dehydrogenase (EC 1.1.1.41) has been purified to homogeneity by the criteria of disc gel electrophoresis and sedimentation equilibrium. Purification of the enzyme is facilitated by the presence of phenylmethanesulfonyl fluoride and by the use of a ribose-linked adenosine 5'-monophosphate affinity column. The enzyme appears to be composed of nonidentical subunits of molecular weights 42 800 and 38 300 as estimated by polyacrylamide gel electrophoresis in 0.1% sodium dodecyl sulfate. From the intensity of each band and the native molecular weight, it is concluded that the enzyme is composed of either six or eight subunits, three or four of each type, respectively. The availability of pure enzyme will allow clarification of the structure of the enzyme by ligand binding studies.
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PMID:Purification and subunit structure of nicotinamide adenine dinucleotide specific isocitrate dehydrogenase from Neurospora crassa. 22 15

8-Bromoadenine nucleotides were tested as potential substrates and/or inhibitors of mitochondrial processes in intact or disrupted organelles, as substrates of various phosphotransferases, and as allosteric effectors in the reactions catalyzed by phosphofructokinase, isocitrate dehydrogenase, glutamate dehydrogenase, and fructose-1,6-bisphosphatase. 8-BrATP and 8-BrADP are not recognized by the translocase system located in the inner mitochondrial membrane and cannot be used as usbstrates in oxidative phosphorylation and related reactions catalyzed be beef heart submitochondrial membranes. This confirms the high specificity for adenine nucleotides of the mammalian systems involved in energy-yielding and energy-requiring reactions. However, 8-BrATP and 8-BrADP are able to substitute for the natural adenine nucleotides in reactions catalyzed by many phosphotransferases, although their capacity as phosphate donors and acceptors is generally much reduced. On the other hand, in almost all investigated cases, the 8-bromoadenine nucleotides have lost the capability of the natural adenine nucleotides to act as allosteric effectors, indicating that the structural requirements for allosteric activity are more stringent than those for catalytic activity.
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PMID:Enzymatic properties of 8-bromoadenine nucleotides. 22 99

Extracts were prepared from Micrococcus cryophilus, several strains of Branhamella catarrhalis and Neisseria spp. Esterases, NADP-dependent isocitrate dehydrogenase and malate dehydrogenase activities were assayed after electrophoresis of extracts of polyacrylamide gels. Except for Neisseria perflava and N. sicca which resolved activity bands for the acetate-esterase only, the remaining bacteria exhibited species-specific esterase patterns also for the propionate and butyrate substrates. The multiple esterase patterns from B. catarrhalis ATCC25238 were qualitatively and quantitatively different from those of B. catarrhalis ATCC23246. This finding and other evidence supports a taxonomic shift of the latter to a species level of that genus. The atypical neisserias N. caviae and N. ovis appeared to exhibit an intrageneric specificity in their esterase patterns with those from B. catarrhalis but not to the other Neisseria spp. tested. The malate dehydrogenase patterns from the atypical neisserias and B. catarrhalis ATCC23246 were qualitatively similar; however, the patterns of isocitrate dehydrogenase activity were variable for these species. Micrococcus cryophilus was distinct in its esterase and dehydrogenase bands, strongly suggesting its taxon unrelatedness to the genus Branhammella or the atypical neisserias. Of the enzymes assayed, esterase proved to be the most reliable for taxonomic identifications.
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PMID:Enzyme electrophoretograms in the analysis of taxon relatedness of Micrococcus cryophilus, Branhamella catarrhalis and atypical Neisserias. 23 7

A temperature-dependent conformational change of the active DPN-linked isocitrate dehydrogenase was observed. When initial reaction kinetic data were examined between 35 and 5 degrees, the Hill number (n) varied from 2 at higher to n approaching unity at lower temperatures, with an inflection point at 17 degrees. The presence of manganous isocitrate in the incubation media shifted the transition temperature for enzyme inactivation by 5,5'-dithiobis(2-nitrobenzoate) from 8-16 degrees. These temperature-dependent transitions were paralleled by progressive changes in sedimentation velocities from s20, w of 10.4 at 25 degrees to 7.3 at 10 degrees as measured by active band centrifugation. The linear Arrhenius plot for apparent V max and the constancy of S0.5 for the substrate manganous isocitrate between 35 and 5 degrees suggest that this temperature-dependent conformational change may not be solely related to manganous isocitrate. Further indications of equilibria between different species of enzyme in solution and effects of substrates and cofactors on conformation came from studies of specific activity of enzyme diluted into buffers at 3 and 25 degrees. Dilution to concentrations between 10 and 25 mum enzyme resulted in relatively rapid protein concentration-dependent inactivation which could be prevented and fully reversed by manganous isocitrate. No further substantial inactivation was found subsequent to this phase at 25 degrees. Lowering the temperature of the dilution buffer to 3 degrees favored formation of enzyme species exhibiting a further time and pH-dependent loss of activity which became independent of protein concentration below 7 mum enzyme. The rate of cold inactivation was reduced by raising the ionic strength of the buffer and its progress could be arrested by manganous isocitrate; however, the substrate did not restore the original activity.
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PMID:Effects of temperature on diphosphopyridine nucleotide-linked isocitrate dehydrogenase from bovine heart. Aspects of the kinetics, stability, and quarternary structure of the enzyme. 23 54

The DPN-specific isocitrate dehydrogenase of pig heart is totally and irreversibly inactivated by 0.05 M potassium cyanate at pH 7.4 A plot of the rate constant versus cyanate concentration is not linear, but rather exhibits saturation kinetics, implying that cyanate may bind to the enzyme to give an enzyme-cyanate complex (K equal 0.125 M) prior to the covalent reaction. In the presence of manganous ion the addition of isocitrate protects the enzyme against cyanate inactivation, indicating that chemical modification occurs in the active site region of the enzyme. The dependence of the decrease of the rate constant for inactivation on the isocitrate concentration yields a dissociation constant for the enzyme-manganese-isocitrate complex which agrees with the Michaelis constant. The allosteric activator ADP, which lowers the Michaelis constant for isocitrate, does not itself significantly affect the cyanate reaction; however, it strikingly enhances the protection by isocitrate. The addition of the chelator EDTA essentially prevents protection by isocitrate and manganous ion, demonstrating the importance of the metal ion in this process. The substrate alpha-ketoglutarate and the coenzymes DPN and DPNH do not significantly affect the rate of modification of the enzymes by cyanate. Incubation of isocitrate dehydrogenase with 14C-labeled potassium cyanate leads to the incorporation of approximately 1 mol of radioactive cyanate per peptide chain concomitant with inactivation. Analysis of acid hydrolysates of the radioactive enzyme reveals that lysyl residues are the sole amino acids modified. These results suggest that cyanate, or isocyanic acid, may bind to the active site of this enzyme as an analogue of carbon dioxide and carbamylate a lysyl residue at the active site.
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PMID:Cyanate modification of essential lysyl residues of the diphosphopyridine nucleotide-specific isocitrate dehydrogenase of pig heart. 23 32


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