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:1.6.5.3 (complex I)
8,901 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of Tinopals (cationic benzoxazoles) AMS-GX and 5BM-GX on NADH-oxidase, NADH:ferricyanide reductase, and NADH --> APAD+ transhydrogenase reactions and energy-linked NAD+ reduction by succinate, catalyzed by NADH:ubiquinone oxidoreductase (Complex I) in submitochondrial particles (SMP), were investigated. AMS-GX competes with NADH in NADH-oxidase and NADH:ferricyanide reductase reactions (K(i) = 1 micro M). 5BM-GX inhibits those reactions with mixed type with respect to NADH (K(i) = 5 micro M) mechanism. Neither compound affects reverse electron transfer from succinate to NAD+. The type of the Tinopals' effect on the NADH --> APAD+ transhydrogenase reaction, occurring with formation of a ternary complex, suggests the ordered binding of nucleotides by the enzyme during the reaction: AMS-GX and 5BM-GX inhibit this reaction uncompetitively just with respect to one of the substrates (APAD+ and NADH, correspondingly). The competition between 5BM-GX and APAD+ confirms that NADH is the first substrate bound by the enzyme. Direct and reverse electron transfer reactions demonstrate different specificity for NADH and NAD+ analogs: the nicotinamide part of the molecule is significant for reduced nucleotide binding. The data confirm the model suggesting that during NADH --> APAD+ reaction, occurring with ternary complex formation, reduced nucleotide interacts with the center participating in NADH oxidation, whereas oxidized nucleotide reacts with the center binding NAD+ in the reverse electron transfer reaction.
...
PMID:Kinetic mechanism of mitochondrial NADH:ubiquinone oxidoreductase interaction with nucleotide substrates of the transhydrogenase reaction. 1260 Feb 70

NADH:ubiquinone oxidoreductase (complex I) is the first enzyme of the mitochondrial electron transport chain and catalyzes the oxidation of beta-NADH by ubiquinone, coupled to transmembrane proton translocation. It contains a flavin mononucleotide (FMN) at the active site for NADH oxidation, up to eight iron-sulfur (FeS) clusters, and at least one ubiquinone binding site. Little is known about the mechanism of coupled electron-proton transfer in complex I. This communication demonstrates how the catalytic fragment of complex I, subcomplex Ilambda, can be adsorbed onto a pyrolytic graphite edge electrode to catalyze the interconversion of NADH and NAD+, with the electrode as the electron acceptor or donor. NADH oxidation and NAD+ reduction are completely reversible and occur without the application of an overpotential. The potential of zero current denotes the potential of the NAD+/NADH redox couple, and the dependence of ENAD+ on pH, and on the NADH:NAD+ ratio, is in accordance with the Nernst equation. The catalytic potential of the enzyme, Ecat, is close to one of the two reduction potentials of the active site FMN and to the potential of a nearby [2Fe - 2S] cluster; therefore, either one or both of these redox couples is suggested to be important in controlling NADH oxidation by complex I.
...
PMID:Reversible, electrochemical interconversion of NADH and NAD+ by the catalytic (Ilambda) subcomplex of mitochondrial NADH:ubiquinone oxidoreductase (complex I). 1278 8

The purpose of the current study was to investigate aspects of improved bioenergetic function using nicotinamide during stroke. Using a global ischemia-reperfusion mouse model, ATP was depleted by 50% in the brain. The use of nicotinamide to provide a large reserve of brain NAD+ restored ATP levels to 61% of control levels. Alternatively, using nicotinamide as a PARP inhibitor restored ATP levels up to 72%. However, using a large reserve of NAD+ in the brain together with PARP inhibition proved to be additive, restoring ATP to 85% of control levels during the first critical 5 min of reperfusion. NAD+ and ATP levels correlated almost exactly. Brain mitochondrial function was also examined after cerebral ischemia-reperfusion. State 3 respiration of complex I was found to be abolished. However, this was a non-permanent inhibition of activity in vitro, since (NADH ubiquinone oxideroductase) complex I activity in these mitochondria was restored upon the addition of NADH. In vivo, the use of increased brain NAD+ and PARP inhibition was able to partially restore mitochondrial respiration. Taken together, the results show that nicotinamide offers a substantial protective role in terms of preservation of cellular ATP and mitochondrial NAD-linked respiration.
...
PMID:Nicotinamide offers multiple protective mechanisms in stroke as a precursor for NAD+, as a PARP inhibitor and by partial restoration of mitochondrial function. 1451 2

Mitochondrial respiratory chain complexes I and III have been shown to produce superoxide but the exact contribution and localization of individual sites have remained unclear. We approached this question investigating the effects of oxygen, substrates, inhibitors, and of the NAD+/NADH redox couple on H2O2 and superoxide production of isolated mitochondria from rat and human brain. Although rat brain mitochondria in the presence of glutamate+malate alone do generate only small amounts of H2O2 (0.04 +/- 0.02 nmol H2O2/min/mg), a substantial production is observed after the addition of the complex I inhibitor rotenone (0.68 +/- 0.25 nmol H2O2/min/mg) or in the presence of the respiratory substrate succinate alone (0.80 +/- 0.27 nmol H2O2/min/mg). The maximal rate of H2O2 generation by respiratory chain complex III observed in the presence of antimycin A was considerably lower (0.14 +/- 0.07 nmol H2O2/min/mg). Similar observations were made for mitochondria isolated from human parahippocampal gyrus. This is an indication that most of the superoxide radicals are produced at complex I and that high rates of production of reactive oxygen species are features of respiratory chain-inhibited mitochondria and of reversed electron flow, respectively. We determined the redox potential of the superoxide production site at complex I to be equal to -295 mV. This and the sensitivity to inhibitors suggest that the site of superoxide generation at complex I is most likely the flavine mononucleotide moiety. Because short-term incubation of rat brain mitochondria with H2O2 induced increased H2O2 production at this site we propose that reactive oxygen species can activate a self-accelerating vicious cycle causing mitochondrial damage and neuronal cell death.
...
PMID:Characterization of superoxide-producing sites in isolated brain mitochondria. 1462 76

Inhibition of complex I has been considered to be an important contributor to mitochondrial dysfunction in tissues subjected to ischemia-reperfusion. We have investigated the role of complex I in a severe energetic deficit that develops in kidney proximal tubules subjected to hypoxia-reoxygenation and is strongly ameliorated by supplementation with specific citric acid cycle metabolites, including succinate and the combination of -ketoglutarate plus malate. NADH: ubiquinone reductase activity in the tubules was decreased by only 26% during 60-min hypoxia and did not change further during 60-min reoxygenation. During titration of complex I activity with rotenone, progressive reduction of NAD+ to NADH was detected at >20% complex I inhibition, but substantial decreases in ATP levels and mitochondrial membrane potential did not occur until >70% inhibition. NAD+ was reduced to NADH during hypoxia, but the NADH formed was fully reoxidized during reoxygenation, consistent with the conclusion that complex I function was not limiting for recovery. Extensive degradation of cytosolic and mitochondrial NAD(H) pools occurred during either hypoxia or severe electron transport inhibition by rotenone, with patterns of metabolite accumulation consistent with catabolism by both NAD+ glycohydrolase and pyrophosphatase. This degradation was strongly blocked by alpha-ketoglutarate plus malate. The data demonstrate surprisingly little sensitivity of these cells to inhibition of complex I and high levels of resistance to development of complex I dysfunction during hypoxia-reoxygenation and indicate that events upstream of complex I are important for the energetic deficit. The work provides new insight into fundamental aspects of mitochondrial pathophysiology in proximal tubules during acute renal failure.
...
PMID:Preservation of complex I function during hypoxia-reoxygenation-induced mitochondrial injury in proximal tubules. 1466 31

The inner mitochondrial membrane is selectively permeable, which limits the transport of solutes and metabolites across the membrane. This constitutes a problem when intramitochondrial enzymes are studied. The channel-forming antibiotic AlaM (alamethicin) was used as a potentially less invasive method to permeabilize mitochondria and study the highly branched electron-transport chain in potato tuber (Solanum tuberosum) and pea leaf (Pisum sativum) mitochondria. We show that AlaM permeabilized the inner membrane of plant mitochondria to NAD(P)H, allowing the quantification of internal NAD(P)H dehydrogenases as well as matrix enzymes in situ. AlaM was found to inhibit the electron-transport chain at the external Ca2+-dependent rotenone-insensitive NADH dehydrogenase and around complexes III and IV. Nevertheless, under optimal conditions, especially complex I-mediated NADH oxidation in AlaM-treated mitochondria was much higher than what has been previously measured by other techniques. Our results also show a difference in substrate specificities for complex I in mitochondria as compared with inside-out submitochondrial particles. AlaM facilitated the passage of cofactors to and from the mitochondrial matrix and allowed the determination of NAD+ requirements of malate oxidation in situ. In summary, we conclude that AlaM provides the best method for quantifying NADH dehydrogenase activities and that AlaM will prove to be an important method to study enzymes under conditions that resemble their native environment not only in plant mitochondria but also in other membrane-enclosed compartments, such as intact cells, chloroplasts and peroxisomes.
...
PMID:Oxidation and reduction of pyridine nucleotides in alamethicin-permeabilized plant mitochondria. 1497 26

The mechanism coupling electron transfer and proton pumping in respiratory complex I (NADH-ubiquinone oxidoreductase) has not been established, but it has been suggested that it involves conformational changes. Here, the influence of substrates on the conformation of purified complex I from Escherichia coli was studied by cross-linking and electron microscopy. When a zero-length cross-linking reagent was used, the presence of NAD(P)H, in contrast to that of NAD+, prevented the formation of cross-links between the hydrophilic subunits of the complex, including NuoB, NuoI, and NuoCD. Comparisons using different cross-linkers suggested that NuoB, which is likely to coordinate the key iron-sulfur cluster N2, is the most mobile subunit. The presence of NAD(P)H led also to enhanced proteolysis of subunit NuoG. These data indicate that upon NAD(P)H binding, the peripheral arm of the complex adopts a more open conformation, with increased distances between subunits. Single particle analysis showed the nature of this conformational change. The enzyme retains its L-shape in the presence of NADH, but exhibits a significantly more open or expanded structure both in the peripheral arm and, unexpectedly, in the membrane domain also.
...
PMID:Substrate-induced conformational change in bacterial complex I. 1503 11

A simple in situ model of alamethicin-permeabilized isolated rat liver mitochondria was used to investigate the channeling of NADH between mitochondrial malate dehydrogenase (MDH) and NADH:ubiquinone oxidoreductase (complex I). Alamethicin-induced pores in the mitochondrial inner membrane allow effective transport of low molecular mass components such as NAD+/NADH but not soluble proteins. Permeabilized mitochondria demonstrate high rates of respiration in the presence of malate/glutamate and NAD+ due to coupled reaction between MDH and complex I. In the presence of pyruvate and lactate dehydrogenase, an extramitochondrial competitive NADH utilizing system, respiration of permeabilized mitochondria with malate/glutamate and NAD+ was completely abolished. These data are in agreement with the free diffusion of NADH and do not support the suggestion of direct channeling of NADH from MDH to complex I.
...
PMID:Absence of NADH channeling in coupled reaction of mitochondrial malate dehydrogenase and complex I in alamethicin-permeabilized rat liver mitochondria. 1514 70

Two types of NADH oxidation, rotenone-sensitive and rotenone-insensitive, in suspension of beef heart mitochondria were investigated by the spectrophotometric method. The oxidation of the added NADH by mitochondria in hypotonic media occurs only through the NADH dehydrogenase of the respiratory chain, since it was totally blocked by rotenone or amytal (and also by antimycin A or azide), but the ferricyanide-activated NADH oxidation was insensitive to these inhibitors. The insensitivity of the NADH dehydrogenase to rotenone appears to be due to a shunt of the electron transfer to ferricyanide without involving of ubiquinone. Both types of the oxydation occur through one and the same enzyme, which exists in two states. The evidence in favour of this is that NAD+ and DTT slightly influence the first type of oxidation but strongly inhibit the second one. The ferricyanide-activated NADH oxidation takes place in NADH dehydrogenase fragments released from mitochondria. Low Ds-Na concentrations block the respiratory chain NADH oxidation but increase the velocity of the ferricyanide-dependent oxidation. Probably, the increase is the result of the detergent-induced additional releasing of the fragments. The express-method for the preparation of the initially purified fraction with a high yield of detergent-containing fragments of the active enzyme is described.
...
PMID:[Rotenone-insensitive NADH oxydation in mitochondrial suspension occurs by NADH dehydrogenase of respiratory chain fragments]. 1552 65

In the yeast Saccharomyces cerevisiae, the most important systems for conveying excess cytosolic NADH to the mitochondrial respiratory chain are the external NADH dehydrogenases (Nde1p and Nde2p) and the glycerol-3-phosphate dehydrogenase shuttle. In the latter system, NADH is oxidized to NAD+ and dihydroxyacetone phosphate is reduced to glycerol 3-phosphate by the cytosolic Gpd1p. Subsequently, glycerol 3-phosphate donates electrons to the respiratory chain via mitochondrial glycerol-3-phosphate dehydrogenase (Gut2p). At saturating concentrations of NADH, the activation of external NADH dehydrogenases completely inhibits glycerol 3-phosphate oxidation. Studies on the functionally isolated enzymes demonstrated that neither Nde1p nor Nde2p directly inhibits Gut2p. Thus, the inhibition of glycerol 3-phosphate oxidation may be caused by competition for the entrance of electrons into the respiratory chain. Using single deletion mutants of Nde1p or Nde2p, we have shown that glycerol 3-phosphate oxidation via Gut2p is inhibited fully when NADH is oxidized via Nde1p, whereas only 50% of glycerol 3-phosphate oxidation is inhibited when Nde2p is functioning. By comparing respiratory rates with different respiratory substrates, we show that electrons from Nde1p are favored over electrons coming from Ndip (internal NADH dehydrogenase) and that when electrons come from either Nde1p or Nde2p and succinodehydrogenase, their use by the respiratory chain is shared to a comparable extent. This suggests a very specific competition for electron entrance into the respiratory chain, which may be caused by the supramolecular organization of the respiratory chain. The physiological consequences of such regulation are discussed.
...
PMID:Competition of electrons to enter the respiratory chain: a new regulatory mechanism of oxidative metabolism in Saccharomyces cerevisiae. 1555 39


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

---