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)

A serum-free, hormone-supplemented medium (SFHM) for maintaining neonatal rat heart cells in culture has been developed in this laboratory (Mohamed et al., 1983). Morphological assessment of heart cells grown in SFHM show it to be similar to commonly used serum-supplemented media. To quantitatively compare cell behavior in SFHM with serum-supplemented media, the activities of ten regulatory enzymes which represent four metabolic pathways were studied in heart cells cultured in SFHM. The enzyme activities which were measured included hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphofructokinase, pyruvate kinase, NAD+-linked sn-glycerol-3-phosphate dehydrogenase, malate dehydrogenase, NAD+-linked isocitrate dehydrogenase, NADH-cytochrome c reductase, and succinic cytochrome c reductase. Rat heart cells maintained in culture on SFHM are not only qualitatively and quantitatively similar to those maintained in serum-supplemented medium but also provide a more suitable model system for metabolic studies of neonatal cardiac tissue for several reasons: 1) many enzyme activities that may represent dedifferentiation are elevated by serum; 2) NAD-linked glycerol-3-phosphate dehydrogenase activity in cells maintained on SFHM is similar to the in vivo activity; 3) cells beat at or near the in vivo frequency and can be maintained 3 months on SFHM; 4) the SFHM is chemically defined and thus can be completely manipulated by the investigator. The effects of three concentrations of hydrocortisone (HC) (5,000 ng/ml, 50 micrograms/ml, 0 ng/ml) on heart cells cultured in SFHM supported our previous conclusion that function (beating) and growth (protein accumulation) are inversely related in cultured neonatal rat heart cells.
...
PMID:Control of enzyme activity levels by serum and hydrocortisone in neonatal rat heart cells cultured in serum-free medium. 674 46

This study has investigated the feasibility of calculating the cytoplasmic free [NADP+]/[NADPH] ratio in rat brain. The time course of the change in the substrate ratios of the malate dehydrogenase (decarboxylating) [E.C. 1.1.1.40], NADP+-isocitrate dehydrogenase (decarboxylating) [E.C. 1.1.1.42] and 6-phosphogluconate dehydrogenase (decarboxylating) [E.C. 1.1.1.44] reactions was followed for up to 10 min after a single, unmodified electroconvulsive seizure. From the results it has been concluded that during periods of low flux, the direction and magnitude of the change in the cytoplasmic free [NADP+]/[NADPH] ratio can, in fact, be reasonably determined even though there is some uncertainty in the absolute value of the ratio itself. It is recommended that reliance not be placed on a single enzyme system but that one or both of the other systems also be observed under a given experimental condition to increase confidence in the determination. The results also demonstrate that seizure and anoxia have a far lesser effect on the cytoplasmic free [NADP+]/[NADPH] ratio than on the free [NAD+]/[NADH] ratio in the same compartment. These results suggest that the pathways using the nicotinamide-adenine dinucleotide phosphate system are relatively protected from the rapid fluctuations that seizure and anoxia can produce.
...
PMID:The calculation of the cytoplasmic free [NADP+]/[NADPH] ratio in brain: effect of electroconvulsive seizure. 679 9

The histochemistry of five dehydrogenases, namely isocitrate, succinate and lactate dehydrogenases and NADH and NADPH diaphorases were studied in the tissues of the schistosome vector snail, Bulinus truncatus, before and after treatment with the molluscicide Frescon. Isocitrate and succinate dehydrogenases showed their strongest activity in the respiratory epithelia, while lactate dehydrogenase showed a high level of activity in the tissues that are known to be capable of glycolysis. Following the administration of Frescon, a marked loss in the activity of isocitrate dehydrogenase and NADPH diaphorase occurred. It is postulated that the molluscicide toxin may interfere with cellular respiration, especially in the exposed areas of the body.
...
PMID:Histochemical studies of some enzymes in the tissues of the schistosome vector snail Bulinus truncatus (Audouin) with special reference to the effects of a molluscicide. I. Dehydrogenases. 689 33

A number of differences in the kinetic and physical properties of the Escherichia coli nicotinamide adenine dinucleotide phosphate (NADP+) dependent malic enzyme have been found, depending upon whether Mg2+ or Mn2+ served to fulfill the divalent cation requirement. The velocity-NADP+ and velocity-cation saturation curves exhibit a simple hyperbolic response in the presence of either metal cofactor, but the affinity for NADP+ (and malate) as well as the Vmax is increased in the presence of Mn2+. The high affinity of the enzyme for Mn2+ coupled with the increased affinity for substrates indicates that Mn2+ is the preferred cofactor in vitro. With either Mg2+ or Mn2+ as cation, the velocity-malate saturation curves in the absence of effectors are complex at pH 7.45, indicating varying combinations of apparent positive and negative cooperative behavior. Greater initial positive cooperative behavior between malate binding sites is observed with Mg2+ as cation. The enzyme appears to be equally sensitive to inhibition by the allosteric inhibitors reduced nicotinamide adenine dinucleotide (NADH) and oxaloacetic acid (OAA) in the presence of either cation, but the interaction between malate binding sites, in the presence of effectors, varies significantly with the choice of metal cofactor. The inhibitor NADH increases the interaction between malate binding sites in the presence of Mn2+ but has little effect on subunit interaction in the presence of Mg2+. The inhibitor OAA increases the interaction between malate binding sites in the presence of both cations, with increased positive cooperativity observed with Mn2+ but increased negative cooperativity with Mg2+. The kinetic data can be explained by a model involving sequential ligand-induced conformational changes of the enzyme, resulting in a mixture of apparent positive and negative cooperative behavior. Alternative explanations involving different classes of noninteracting binding sites or different enzyme forms are also considered. The metal cofactors, Mg2+ and Mn2+, appear to stabilize two distinct conformational states of the enzyme which differ in response to varying substrate and effector concentrations. Altered conformational states of the enzyme in the presence of the two cations are further substantiated by proteolytic digestion studies with the homogeneous enzyme. The results are strikingly similar to previous results reported on the nicotinamide adenine dinucleotide (NAD+) dependent malic enzyme and the NAD+-dependent isocitrate dehydrogenase, supporting the suggestion that metal cofactors function as regulatory entities.
...
PMID:Role of metal cofactors in enzyme regulation. Differences in the regulatory properties of the Escherichia coli nicotinamide adenine dinucleotide phosphate specific malic enzyme, depending on whether magnesium ion or manganese ion serves as divalent cation. 701 78

The activity of 22 enzymes of energy metabolism was determined in m. vastus lateralis quadricipitis of 14 adolescents aged 13-15 years (7 girls) and 14 adults aged 22 to 42 years (7 female subjects). The measurements were performed kinetically, at 37 degrees C, using optimal or near-to-optimal procedures. With the exception of one enzyme, enolase, no differences between sexes were observed in the two age groups. Glycolytic enzymes, including fructose-6-phosphate kinase, showed no significant differences in their activity in adults as compared to adolescents. The activity of enolase was lower in females of both age groups, but no difference due to age was found in this respect. Of the oxidative enzymes studied, only citrate synthase showed no significant difference in adults vs adolescents, whereas the activities of lipoamide dehydrogenase (+ 40%), NADP-isocitrate dehydrogenase (+ 44%), fumarase (+ 24.5%), total malate dehydrogenase (+ 42.2%) and NADH-dehydrogenase (+ 39%) were all significantly higher in the latter group. Aspartate aminotransferase was also 44% higher in adolescents. The possible physiological importance of these observations is discussed with regard to the functional capacity of the skeletal muscle. The hypothesis was considered that adolescents of this age may have a glycolytic capacity comparable to adults, but that they may oxidize pyruvate at a rate higher than adults.
...
PMID:Enzyme activities in skeletal muscle of 13-15 years old adolescents. 705 78

Binding of NADH and NADPH to NAD-linked isocitrate dehydrogenase from pig heart (which contains three types of subunits of similar molecular weight in the ratio 2:1:1) was studied by use of the enhancement of nucleotide fluorescence. NADH and NADPH bind independently and, for both reduced nucleotides, 0.5 binding sites/average subunit or two binding sites for every four subunits were detected. Binding of NADH is unaffected by metal ion, isocitrate, or NAD+. ADP is also not competitive with NADH binding but reduces the strength of binding 3-fold. In contrast, ATP (KI = 9 microM ATP4-) appears to be competitive with NADH. Evidence for an NADH site with higher dissociation constant (KD greater than 200 microM) than that obtained from the fluorescence measurements (KD = 2.8 microM at pH 6.1) is indicated by competition of NADH with [14C]NAD+ binding. NADPH binding is enhanced by the presence of manganese. The metal dependence is consistent with NADPH (KD = 8.1 microM at pH 6) binding to the same site as Mn-NADPH2- (KD = 0.9 microM). Dissociation constants for both species increase with increasing pH in the range 6-8. NADPH binding is competitively inhibited by ADP, ATP, ADP-ribose, and isocitrate. This inhibition of NADPH binding is probably indirect since measurements of [14C]ADP in the presence and absence of NADPH showed little inhibition of binding by NADPH concentrations sufficient to saturate the fluorescent site. These studies extent the number of ligands for isocitrate dehydrogenase for which there are fewer binding sites than there are subunits.
...
PMID:Interrelationships among nucleotide binding sites of pig heart NAD-dependent isocitrate dehydrogenase. 706 63

The chain oxidation of glyceraldehyde-3-phosphate dehydrogenase.NADH by perhydroxyl radicals and propagated by molecular oxygen was studied by the xanthine-xanthine oxidase system, 60Co gamma-ray, and pulse radiolysis. The chain length, amount of NADH oxidized per HO2 generated, increases with increasing acidity of the medium and reaches a value of 73 at pH 5.0. The rate constant for the oxidation of the glyceraldehyde-3-phosphate dehydrogenase.NADH complex by HO2 was estimated to be 2 X 10(7) M-1 S-1 at ambient temperatures (23-24 degrees C). Rate studies as a function of pH indicate that O2- is unreactive toward the glyceraldehyde-3-phosphate dehydrogenase.NADH complex. Other dehydrogenases (malate dehydrogenase, glutamate dehydrogenase, and isocitric dehydrogenase) studied showed no catalytic activity in the oxidation of NADH by HO2/O2-.
...
PMID:Glyceraldehyde-3-phosphate dehydrogenase-catalyzed chain oxidation of reduced nicotinamide adenine dinucleotide by perhydroxyl radicals. 718 97

The paper deals with the intensity of NADPH formation in the isocytrate dehydrogenase reaction and NADPH oxidation in the lactate and malate dehydrogenase reactions. It is shown that bicarbonate, phosphate, acetate, chloride and triethanolamine buffer in concentrations of 1 . 10(-1) = 4 . 10(-1) M can inhibit these processes intensity. The inhibitory effect of the mentioned anions on the NADH-isocytrate dehydrogenase activity is considerably decreased when adding MnCl2 or MgCl2 to the incubation medium. Sucrose is established to inhibit the formation of NADPH in the isocitrate dehydrogenase reaction at 2 . 10(-1) M and higher.
...
PMID:[Effect of bicarbonate and certain anions on NADP redox]. 738 74

The sigmoid dependence of the initial rate of the reaction catalysed by NAD+-dependent isocitrate dehydrogenase on the concentration of isocitrate is greatly reduced as the pH is decreased. The apparent pK for this process is 7.3. At pH values of 6.0 and 6.5 the enzyme exhibits hyperbolic kinetics with respect to isocitrate at relatively high concentrations of NAD+, but the dependence becomes sigmoid at lower NAD+ concentrations. The allosteric activators ADP and citrate have only small effects on the activity of the enzyme at pH 6.5 but in the latter case the effects are increased by decreasing the concentration of NAD+. The dependence of initial velocity on the NAD+ concentration is hyperbolic at all pH values in the pH range 6--8.5. NADH is a competitive inhibitor of enzyme activity with respect to NAD+, and its presence induces a sigmoid dependence of initial velocity on isocitrate concentration at pH 6.5 and in the presence of high concentrations of NAD+. Kinetic studies at pH 6.5 indicate that the apparent maximum velocity of the reaction with respect to NAD+ is insensitive to changes in the isocitrate concentration and that with isocitrate as the substrate is relatively insensitive to changes in the NAD+ concentration under conditions where the behaviour appears to be hyperbolic. threo-Ds-Isocitrate is the true substrate for the enzyme and the corresponding Ls isomer is neither a substrate nor an inhibitor.
...
PMID:The effect of pH on the allosteric behaviour of ox-brain NAD+-dependent isocitrate dehydrogenase. 740 93

The effect of inhibition of NADP-specific isocitrate dehydrogenase (EC 1.1.1.42) by DL-threo-alpha-methylisocitrate (3-hydroxy-1,2,3-butanetricarboxylase) on urea synthesis was studied in isolated rat hepatocytes. alpha-Methylisocitrate substantially inhibited the rate of urea synthesis (35--84%) with substrates requiring net reductive amination of 2-oxoglutarate to glutamate for aspartate synthesis (i.e., L-serine, D-alanine, or NH4Cl + L-lactate). alpha-Methylisocitrate did not inhibit synthesis of urea from substrates not requiring reductive formation of glutamate (i.e. L-alanine, L-glutamine, L-asparagine, or NH4Cl + L-ornithine). The rate-limiting role of NADPH in urea synthesis was correlated with the decrease in NADPH content that occurred upon addition of NH4Cl or of alpha-methylisocitrate to hepatocytes incubated with lactate and pyruvate, indicating utilization of NADPH for reductive amination of 2-oxoglutarate and inhibition of NADPH generation via NADP-isocitrate dehydrogenase, respectively. Similar results were obtained with D-alanine and L-serine; however, alpha-methylisocitrate or NH4Cl did not substantially decrease NADPH content when L-alanine was the substrate. Inhibitors or ornithine--2-oxo acid transaminase (L-canaline or gabaculine) decreased the uptake of ornithine by hepatocytes and inhibited the alpha-methylisocitrate insensitive urea synthesis from ornithine and NH4Cl. Canaline did not inhibit urea synthesis from lactate, ornithine, and NH4Cl but the inhibition by alpha-methylisocitrate of urea formation from this combination was appreciably larger with canaline (approx. 82%) than without canaline (approx. 48%). Inhibition of urea synthesis from NH4Cl + lactate by alpha-methylisocitrate was partially prevented by oleate, octanoate, or 3-hydroxybutyrate. When the NADH content of hepatocytes was increased by 3-hydroxybutyrate, the addition of NH4Cl and/or alpha-methylisocitrate caused a decline in NADH (and NADPH) content, suggesting that reducing equivalents from NADH as well as from NADPH can support net reductive amination of 2-oxoglutarate when required for urea synthesis.
...
PMID:NADP-specific isocitrate dehydrogenase in regulation of urea synthesis in rat hepatocytes. 747 71


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---