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

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

Neutrophil myeloperoxidase, hydrogen peroxide, and chloride constitute a potent antimicrobial system with multiple effects on microbial cytoplasmic membranes. Among these is inhibition of succinate-dependent respiration mediated, principally, through inactivation of succinate dehydrogenase. Succinate-dependent respiration is inhibited at rates that correlate with loss of microbial viability, suggesting that loss of respiration might contribute to the microbicidal event. Because respiration in Escherichia coli can be mediated by dehydrogenases other than succinate dehydrogenase, the effects of the myeloperoxidase system on other membrane dehydrogenases were evaluated by histochemical activity stains of electrophoretically separated membrane proteins. Two bands of succinate dehydrogenase activity proved the most susceptible to inactivation with complete loss of staining activity within 20 min, under the conditions employed. A group with intermediate susceptibility, consisting of lactate, malate, glycerol-3-phosphate, and dihydroorotate dehydrogenases as well as three bands of glucose-6-phosphate dehydrogenase, was almost completely inactivated within 30 min. The relatively resistant group, including the dehydrogenases for glutamate, NADH, and NADPH and the remaining bands of glucose-6-phosphate dehydrogenase, retained substantial amounts of diaphorase activity for up to 60 min of incubation with the myeloperoxidase system. The differential effects of myeloperoxidase on dehydrogenase inactivation could not be correlated with published enzyme contents of flavin or iron-sulfur centers, potential targets of myeloperoxidase-derived oxidants. Despite the relative resistance of NADH dehydrogenase/diaphorase activity to myeloperoxidase-mediated inactivation, electron transport particles prepared from E. coli incubated for 20 min with the myeloperoxidase system lost 55% of their NADH oxidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Differential inactivation of Escherichia coli membrane dehydrogenases by a myeloperoxidase-mediated antimicrobial system. 169 36

[18F]Fluoromisonidazole (1-(3-[18F]fluoro-2-hydroxypropyl)-2-nitroimidazole, [18F]FMISO) is a nitroimidazole compound that is being used as a new imaging agent for hypoxia. Because its uptake in hypoxic tissue is dependent on reduction of the nitro group on the imidazole ring, it is necessary to verify the availability of nitroreductase enzymes in a variety of tissues. FMISO reduction was studied using chemical and enzymatic reducing systems and mammalian cells. FMISO reduction by iron/HCl eliminated the absorbance peak at 325 nm caused by the nitro group. FMISO reduction by xanthine oxidase, as measured by a decrease in absorbance at 325 nm, occurred at a rate of 2.4 +/- 0.3 nmol/min/unit enzyme (mean +/- SEM, N = 15). This reaction was inhibited by allopurinol. Separation of the parent drug from its reduction product following chemical and enzymatic reductions indicated that iron/HCl reduced the majority of the FMISO molecules present, while xanthine oxidase did not. Reduction of FMISO by NADH dehydrogenase could not be demonstrated spectrophotometrically. Measurement of the reduction of FMISO in V79 cells based on the binding of [3H]FMISO to cellular macromolecules was performed using a cell suspension in a three-neck flask. Hypoxic V79 cells bound [3H]FMISO at the rate of 0.26 +/- 0.07 pmol/10(6) cells/min (N = 8). When specific inhibitors of two nitroreductase enzymes and a general inhibitor of electron transport were added to the cell suspension, no consistent, statistically significant inhibition of FMISO binding could be shown. We conclude that while inhibition of FMISO reduction by a purified nitroreductase can be shown, nitroreductase activity in cells is not inhibited so easily. This supports the hypothesis that nitroreductases are plentiful and will not limit the rate of FMISO reduction and uptake in hypoxic tumors or nonmalignant tissues.
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PMID:Reduction of fluoromisonidazole, a new imaging agent for hypoxia. 176 22

Mercuric ion (Hg(II)) causes oxidative tissue damage in kidney cortical cells. We studied the in vitro effects of Hg(II) on hydrogen peroxide (H2O2) production by rat kidney mitochondria, a principal intracellular target of Hg(II). In mitochondria supplemented with a respiratory chain substrate (succinate or malate/glutamate) and an electron transport inhibitor (antimycin A (AA) or rotenone), Hg(II) (30 nmol/mg protein) increased H2O2 formation approximately 4-fold at the ubiquinone-cytochrome b region (AA-inhibited) and 2-fold at the NADH dehydrogenase region (rotenone-inhibited). Concomitantly, Hg(II) increased iron-dependent lipid peroxidation 3.5-fold at the NADH dehydrogenase region, but only by 25% at the ubiquinone-cytochrome b region. The mitochondrial concentration of reduced glutathione (GSH) decreased both with incubation time and Hg(II) concentration. Hg(II), at a concentration of 12 nmol/mg protein, caused almost complete depletion of measurable GSH in substrate-supplemented mitochondria after a 30-min incubation. In electron transport-inhibited mitochondria, Hg(II) caused greater depletion of GSH in rotenone-inhibited than in AA-inhibited mitochondria, consistent with the effects of Hg(II) on lipid peroxidation. These results suggest that Hg(II) at low concentrations depletes mitochondrial GSH and enhances H2O2 formation in kidney mitochondria under conditions of impaired respiratory chain electron transport. The increased H2O2 formation by Hg(II) may lead to oxidative tissue damage, such as lipid peroxidation, observed in mercury-induced nephrotoxicity.
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PMID:Mercury-induced H2O2 production and lipid peroxidation in vitro in rat kidney mitochondria. 176 76

Mitochondrial NADH:ubiquinone oxidoreductase (complex I) is the most complicated enzyme in the respiratory chain and is composed of at least 26 distinct polypeptides. Two hydrophilic subfractions of bovine heart complex I were systematically resolved into individual polypeptides by chromatography. Three polypeptides (51, 24, and 9 kDa) were isolated from the flavoprotein fraction (FP) of complex I, and the complete amino acid sequence of the 9 kDa polypeptide was determined. The 9 kDa polypeptide is composed of 75 amino acids with a molecular weight of 8,437. This protein exhibits no obvious sequence similarity to other proteins. The iron-sulfur protein fraction (IP) of complex I was separated into eight polypeptides, 75, 49, 30, 20, 18, 15, 13 kDa-A, and 13 kDa-B. The 20 kDa polypeptide was recognized as a novel component of IP for the first time. The N-terminal and several peptide sequences of the 20 kDa polypeptide were determined. Comparison of the sequences revealed significant sequence similarities of the 20 kDa polypeptide to the psbG gene products encoded in the chloroplast genome. The conserved sequence in these proteins was also found in the small subunit of the nickel-containing hydrogenases. These results suggest that complex I is related to other redox enzyme complexes.
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PMID:The amino acid sequence of the 9 kDa polypeptide and partial amino acid sequence of the 20 kDa polypeptide of mitochondrial NADH:ubiquinone oxidoreductase. 177 79

The cause of dopamine cell death in Parkinson's disease remains unknown. Present interest centres on the possible involvement of a toxin mediated mechanism such as that produced, by MPTP. In post-mortem studies there is evidence in the substantia nigra for an on-going toxic process involving increased lipid peroxidation, altered iron metabolism and impairment of mitochondrial function at the level of complex I. Although the precise relationship between these biochemical changes is not known, present evidence points to oxidative stress as an important factor contributing to neuronal loss. Altered mitochondrial function and increased iron levels may not initiate Parkinson's disease but rather act to accelerate cell death. Future strategies for the treatment of Parkinson's disease should be aimed at preventing oxidative stress and stopping or slowing the progression of the underlying pathology.
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PMID:Oxidative stress as a cause of Parkinson's disease. 180 37

The primary structures of the nuclear-encoded 51 kDa and 78 kDa subunits of the respiratory chain NADH: ubiquinone reductase (complex I) from Neurospora crassa mitochondria were determined by sequencing cDNA and the N-terminus of the mature proteins. Both subunits are related to the soluble NAD-reducing hydrogenase of the bacterium Alcaligenes eutrophus. Sequence comparison between these subunits, the corresponding subunits of the bovine complex I and the bacterial NAD-reducing hydrogenase further confirms the binding sites of NAD(H), FMN and three iron-sulfur clusters.
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PMID:Primary structures of two subunits of NADH: ubiquinone reductase from Neurospora crassa concerned with NADH-oxidation. Relationship to a soluble NAD-reducing hydrogenase of Alcaligenes eutrophus. 183 16

Purified ubiquinol-cytochrome c reductase of beef heart mitochondria is very stable in aqueous solution; it suffers little damage upon illumination with visible light under aerobic or anaerobic conditions. However, it is rapidly inactivated when the photosensitizer hematoporphyrin is present during illumination. The hematoporphyrin-promoted photoactivation is dependent on sensitizer dose, illumination time, and oxygen. Singlet oxygen is shown to be the destructive agent in this system. The photoinactivation of ubiquinol-cytochrome c reductase is prevented by excess exogenous ubiquinone, regardless of its redox state. This protective effect is not due to protein-ubiquinone interactions but to the singlet oxygen scavenger property of ubiquinone. Ubiquinone also protects against hematoporphyrin-promoted photoinactivation of succinate-ubiquinone reductase and cytochrome c oxidase. The photoinactivation site in ubiquinol-cytochrome c reductase is the iron-sulfur cluster of Rieske's protein. Two histidine residues, presumably serving as two ligands for the iron-sulfur cluster of Rieske's protein, are destroyed. No polypeptide bond cleavage is detected. Photoinactivation has little effect on the spectral properties of cytochromes b and c1 but alters their reduction rates substantially. this photoinactivation also causes the formation of proton-leaking channels in the complex. When the photoinactivated reductase is co-inlaid with intact ubiquinol-cytochrome c reductase or cytochrome c oxidase in a phospholipid vesicle, no proton ejection can be detected during the oxidation of their corresponding substrates.
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PMID:Hematoporphyrin-promoted photoinactivation of mitochondrial ubiquinol-cytochrome c reductase: selective destruction of the histidine ligands of the iron-sulfur cluster and protective effect of ubiquinone. 184 89

In cattle, 7 of the 30 or more subunits of the respiratory enzyme NADH:ubiquinone reductase (complex I) are encoded in mitochondrial DNA, and potential genes (open reading frames, orfs) for related proteins are found in the chloroplast genomes of Marchantia polymorpha and Nicotiana tabacum. Homologues of the nuclear-coded 49- and 23-kDa subunits are also coded in chloroplast DNA, and these orfs are clustered with four of the homologues of the mammalian mitochondrial genes. These findings have been taken to indicate that chloroplasts contain a relative of complex I. The present work provides further support. The 30-kDa subunit of the bovine enzyme is a component of the iron-sulfur protein fraction. Partial protein sequences have been determined, and synthetic oligonucleotide mixtures based on them have been employed as hybridization probes to identify cognate cDNA clones from a bovine library. Their sequences encode the mitochondrial import precursor of the 30-kDa subunit. The mature protein of 228 amino acids contains a segment of 57 amino acids which is closely related to parts of proteins encoded in orfs 169 and 158 in the chloroplast genomes of M. polymorpha and N. tabacum. Moreover, the chloroplast orfs are found near homologues of the mammalian mitochondrial genes for subunit ND3. Therefore, the plant chloroplast genomes have at least two separate clusters of potential genes encoding homologues of subunits of mitochondrial complex I. The bovine 30-kDa subunit has no extensive sequences of hydrophobic amino acids that could be folded into membrane-spanning alpha-helices, and although it contains two cysteine residues, there is no clear evidence in the sequence that it is an iron-sulfur protein.
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PMID:The 30-kilodalton subunit of bovine mitochondrial complex I is homologous to a protein coded in chloroplast DNA. 189 21

Bovine mitochondrial NADH-ubiquinone reductase (complex I), the first enzyme in the electron-transport chain, is a membrane-bound assembly of more than 30 different proteins, and the flavoprotein (FP) fraction, a water-soluble assembly of the 51-, 24-, and 10-kDa subunits, retains some of the catalytic properties of the enzyme. The 51-kDa subunit binds the substrate NAD(H) and probably contains both the cofactor, FMN, and also a tetranuclear iron-sulfur center, while a binuclear iron-sulfur center is located in the 24- or 10-kDa proteins. The 75-kDa subunit is the largest of the six proteins in the iron-sulfur protein (IP) fraction, and its sequence indicates that it too contains iron-sulfur clusters. Partial protein sequences have been determined at the N-terminus and at internal sites in the 51-kDa subunit, and the corresponding cDNA encoding a precursor of the protein has been isolated by using a novel strategy based on the polymerase chain reaction. The mature protein is 444 amino acids long. Its sequence, and those of the 24- and 75-kDa subunits, shows that mitochondrial complex I is related to a soluble NAD-reducing hydrogenase from the facultative chemolithotroph Alcaligenes eutrophus H16. This enzyme has four subunits, alpha, beta, gamma, and delta, and the alpha gamma dimer is an NADH oxidoreductase that contains FMN. The gamma-subunit is related to residues 1-240 of the 75-kDa subunit of complex I, and the alpha-subunit sequence is a fusion of homologues of the 24- and 51-kDa subunits, in the order N- to C-terminal. The most highly conserved regions are in the 51-kDa subunit and probably form parts of nucleotide binding sites for NAD(H) and FMN. Another conserved region surrounds the sequence motif CysXXCysXXCys, which is likely to provide three of the four ligands of a 4Fe-4S center, possibly that known as N-3. Characteristic ligands for a second 4Fe-4S center are conserved in the 75-kDa and gamma-subunits. This relationship with the bacterial enzyme implies that the 24- and 51-kDa subunits, together with part of the 75-kDa subunit, constitute a structural unit in mitochondrial complex I that is concerned with the first steps of electron transport.
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PMID:Relationship between mitochondrial NADH-ubiquinone reductase and a bacterial NAD-reducing hydrogenase. 190 Jan 94

The chloroplast genomes of Marchantia polymorpha, Nicotiana tabacum, and Oryza sativa contain open reading frames (ORFs or potential genes) encoding homologues of some of the subunits of mitochondrial NADH:ubiquinone oxidoreductase (complex I). Seven of these subunits (ND1-ND4, ND4L, ND5, and ND6) are products of the mitochondrial genome, and two others (the 49- and 30-kDa components of the iron-sulfur protein fraction) are nuclear gene products. These findings have been taken to indicate the presence in chloroplasts of an enzyme related to complex I, possibly an NAD(P)H:plastoquinone oxidoreductase, participating in chlororespiration. This view is reinforced by the present work in which we have shown that chloroplast genomes encode a homologue of the 23-kDa subunit, another nuclear-encoded component of bovine complex I. The 23-kDa subunit is in the hydrophobic protein fraction of the enzyme, the residuum after removal of the flavoprotein and iron-sulfur protein fractions. The sequence motif CysXXCysXXCysXXXCysPro, which provides ligands for tetranuclear iron-sulfur centers in ferredoxins, occurs twice in its polypeptide chain and is evidence of two associated 4Fe-4S clusters. This is the only iron-sulfur protein identified so far in the hydrophobic protein fraction of complex I, and so it is possible that one of these centers is that known as N-2, the donor of electrons to ubiquinone. The sequence of the 23-kDa subunit is closely related to potential proteins, which also contain the cysteine-rich sequence motifs, encoded in the frxB ORFs in chloroplast genomes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A homologue of a nuclear-coded iron-sulfur protein subunit of bovine mitochondrial complex I is encoded in chloroplast genomes. 190 Oct 22


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