Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of three calcium antagonists--nifedipin (NF), verapamil (V) and diltiazem (DL)--on the duration of hexobarbital (HB) sleeping time and on monooxygenase activity are studied. The drugs are applied in oral doses of 50, 40 and 30 mg/kg, respectively every day for 3 weeks on male albino rats. NF was found to shorten the duration of HB sleep, to increase the activities of EMD, BPD, AH, ECOD, EROD, NADPH-cytochtome P-450 reductase and the content of cytochrome P-450, and it does not change significantly the content of cytochrome b 5. It increases AD hydroxylation in positions 7-alpha-, 16-beta-, 16-alpha- and 6-beta, which suggests indirectly that NF has probably induced the synthesis of cytochrome P-450a, cytochrome P-450b, cytochrome P-450h and cytochrome P-450p, respectively. Verapamil also shortens the duration of HB sleeping time, increases the activities of EMD, BPD, AH, EROD and NADPH-cytochrome P-450 reductase, not changing the cytochrome P-450 content and the ECOD activity. It increases AD hydroxylation in positions 7-alpha- and 16-alpha-, which suggests probable induction of the synthesis of cytochrome P-450a and cytochrome P-450h. Unlike the other two calcium antagonists, diltiazem slightly shortens the duration of HB sleeping, not changing the enzyme activities studied, the content of cytochrome P-450 and cytochrome b 5, but increases the activities of EROD and NADPH-cytocrome P-450 reductase. It increases AD hydroxylation in positions 7-alpha-, 16-alpha- and 6-beta, which suggests probable induction of cytochrome P-450a, cytochrome P-450h and cytochrome P-450p.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Liver monooxygenase activity after multiple application of nifedipin, verapamil and diltiazem. 213 Jun 25

The effects of butylated hydroxyanisole (BHA), a commonly used food antioxidant, on oxygen consumption, ATPase activity, and the redox state of some electron carriers of rat liver mitochondria have been studied. It was observed that BHA slightly stimulated state 4 respiration but strongly inhibited ADP- and uncoupler-stimulated respiration on NAD(+)- and FAD-linked substrates. ATPase activity and vectorial H+ ejection were affected only slightly by BHA, suggesting that BHA predominantly inhibits mitochondrial electron flow. Experiments to determine its site of action showed that BHA did not noticeably affect electron flow through cytochrome oxidase; in contrast, NADH:duroquinone reductase activity and electron flow through ubiquinone-cytochrome b-cytochrome c complex were inhibited strongly because the oxidation of duroquinol was affected markedly. The BHA block of electron transport was bypassed by both N,N,N',N'-tetramethyl-p-phenylenediamine and 2,6-dichlorophenolindophenol. Also, the presence of BHA changed the redox state of cytochrome b and c1 to a more oxidized level. These observations suggest that electron transport is inhibited by BHA at the NADH-ubiquinone and at the ubiquinone-cytochrome b levels. From Hill plots, it is clear that more than one binding site is involved in complete inhibition; in addition, available evidence suggests that there may be two sites at the substrate side of ubiquinone and another two sites at the oxygen side of ubiquinone. Consequently, mitochondrial ATP synthesis would be interrupted. This event could be related to the toxicity of BHA.
 ...
PMID:Effect of butylated hydroxyanisole on electron transport in rat liver mitochondria. 214 54

The ubiquinol:cytochrome c reductase activity of Paracentrotus lividus mitochondria is relatively insensitive to the specific inhibitors myxothiazol and mucidin. The I50 of myxothiazol and mucidin are three and two orders of magnitude higher, respectively, in P. lividus than in bovine heart mitochondria. The natural resistance of the P. lividus reductase to these inhibitors can be correlated with a single amino replacement, an alanine for a glycine at position 143, in the sequence of cytochrome b. This position is located in a conserved region of the molecule, believed to be important in the oxidation of ubiquinol by the reductase.
 ...
PMID:The cytochrome b of the sea urchin Paracentrotus lividus is naturally resistant to myxothiazol and mucidin. 215 21

Higher plant nitrate reductase can be divided into three functional domains representing its prosthetic groups: 1) flavin; 2) cytochrome b; and 3) Mo-pterin. The flavin domain has been synthesized by heterologous expression in Escherichia coli using a fragment of a corn leaf NADH:nitrate reductase cDNA clone, Zmnr1, which we had previously isolated and sequenced. A Xho2-BamH1 fragment was cut from Zmnr1, containing the sequence for the flavin domain, and ligated in the BamH1 site of expression vector pET3c. When this construct was expressed in E. coli, a 30 kD polypeptide was found to be newly synthesized. The flavin domain was purified to homogeneity using blue Sepharose and shown to have a molecular weight of 30 kD. The recombinant flavin domain has a ferricyanide reductase specific activity of 1000 mumols NADH oxidized/min/mg protein and a visible spectrum virtually identical to that of human NADH:cytochrome b5 reductase.
 ...
PMID:High-level expression in Escherichia coli of the catalytically active flavin domain of corn leaf NADH:nitrate reductase and its comparison to human NADH:cytochrome B5 reductase. 218 8

The arrangement and function of the redox centers of the mammalian bc1 complex is described on the basis of structural data derived from amino acid sequence studies and secondary structure predictions and on the basis of functional studies (i.e., EPR data, inhibitor studies, and kinetic experiments). Two ubiquinone reaction centers do exist--a QH2 oxidation center situated at the outer, cytosolic surface of the cristae membrane (Q0 center), and a Q reduction center (Qi center) situated more to the inner surface of the cristae membrane. The Q0 center is formed by the b-566 domain of cytochrome b, the FeS protein, and maybe an additional small subunit, whereas the Qi center is formed by the b-562 domain of cytochrome b and presumably the 13.4 kDa protein ("QP-C"). The "Q binding proteins" are proposed to be protein subunits of the Q reaction centers of various multiprotein complexes. The path of electron flow branches at the Q0 center, half of the electrons flowing via the high-potential cytochrome chain to oxygen and half of the electrons cycling back into the Q pool via the cytochrome b path connecting the two Q reaction centers. During oxidation of QH2, 2H+ are released to the cytosolic space and during reduction of Q, 2H+ are taken up from the matrix side, resulting in a net transport across the membrane of 2H+ per e- flown from QH2 to cytochrome c, the H+ being transported across the membrane as H (H+ + e-) by the mobile carrier Q. The authors correct their earlier view of cytochrome b functioning as a H+ pump, proposing that the redox-linked pK changes of the acidic groups of cytochrome b are involved in the protonation/deprotonation processes taking place during the reduction and oxidation of Q. The reviewers stress that cytochrome b is in equilibrium with the Q pool via the Qi center, but not via the Q0 center. Their view of the mechanisms taking place at the reductase is a Q cycle linked to a Q-pool where cytochrome b is acting as an electron pump.
 ...
PMID:Organization and function of cytochrome b and ubiquinone in the cristae membrane of beef heart mitochondria. 242 49

The circular dichroism (CD) of dihaem cytochrome b from mitochondrial and bacterial ubiquinol:cytochrome-c reductase (bc1 complex) has been characterized. The dichroic properties of the yeast purified cyt b are very similar to those of the native cyt b within the mitochondrial bc1 complex. The CD spectra in the Soret region of the native cytochrome b present in all species studied show an intense bisignate Cotton effect having a zero-crossing wavelength close to the absorbance maximum. In preparations partially or completely depleted of the low-potential b haem (b1) the CD spectra exhibit a single positive Cotton effect resembling the corresponding absorption spectrum. This is particularly evident in the purified cytochrome b-562 from Rhodobacter sphaeroides R26, which contains only the high-potential b haem (bh). These spectral features together with the reconstitution of the cytochrome b1 haem have been used to resolve the CD contribution of each haem to the CD spectra of cytochrome b. The mechanisms which might be responsible for the optical activity have been examined. It appears that the CD spectra of cytochrome b derive from both the mutual interaction of its two haems (giving rise to exciton coupling) and to the interaction of each haem with nearby aromatic residues, other than the pairs of histidines which coordinate the iron. The dipole coupling between haem and aromatic residues appears to be more important than exciton coupling in the CD spectra of oxidized b cytochromes and correlations have been made between the CD features and the proposed structure of cytochrome b.
 ...
PMID:Circular dichroic spectroscopy of membrane haemoproteins. The molecular determinants of the dichroic properties of the b cytochromes in various ubiquinol:cytochrome c reductases. 254 73

The cytochrome b/c1 complex is an ubiquitous energy transducing enzyme, part of the electron transport chain of prokaryotes, mitochondria, and chloroplasts (b6/f). In the ancient purple photosynthetic bacteria, the b/c1 complex occupies a central metabolic role, being part of their photosynthetic and respiratory electron transport chain. In Rhodobacter the three subunits of the b/c1 complex are FeS protein, cytochrome b, and cytochrome c1, and they are encoded by a constitutively expressed operon named fbc. The organization of the genes for the cytochrome b/c1 complex, the modality of transcription, and the biogenesis of the encoded polypeptides will be described. The Rhodobacter species used to isolate the fbc genes, previously reported as R. sphaeroides was identified as R. capsulatus. Further biochemical characterization of the prokaryotic b/c1 complex indicated that the three polypeptides encoded by the fbc operon comprise the entire catalytic structure: ubiquinol-cytochrome-c reductase. The amino acid sequences of the three b/c1 subunits from the photosynthetic bacterium Rhodobacter capsulatus were compared with the corresponding sequences from yeast mitochondria and spinach chloroplasts. The high homology found between the sequences of all three redox polypeptides from R. capsulatus and yeast mitochondria (cytochrome b 41%, FeS protein 46%, cytochrome c1 31%) provided further evidence that mitochondria arose from the phylogenetic line of purple bacteria. The structure of cytochrome b also exhibited considerable homology to chloroplast cytochrome b6 plus subunit IV (26%). The amino acid sequence of the Rieske FeS protein from R. capsulatus and chloroplasts were found to be conserved only in the C-terminal part (14% total identity), whereas the homology between cytochrome c1 and cytochrome f is very weak (12%), despite similar topology of the two polypeptides. Analysis of the homology suggested that the catalytic sites quinol oxidase (Q0) and quinone reductase (Qi) arose monophonetically, whereas cytochrome c and plastocyanin reductase sites are not homologous and could derive from diverse ancestral genes by convergent evolution.
 ...
PMID:Organization and structure of the genes for the cytochrome b/c1 complex in purple photosynthetic bacteria. A phylogenetic study describing the homology of the b/c1 subunits between prokaryotes, mitochondria, and chloroplasts. 283 Nov 86

A simple procedure for preparation of highly purified soluble succinate-ubiquinone reductase from bovine heart mitochondrial particles is described. The enzyme exhibits four major bands on sodium dodecyl sulfate gel electrophoresis and contains (nmol per mg protein): covalently bound flavin, 6; non-heme iron, 53; acid-labile sulfur, 50; cytochrome b-560 heme, 1.2. The enzyme catalyzes thenoyltrifluoroacetone, or carboxin-sensitive (pure non-competitive with Q2) reduction of Q2 by succinate with a turnover number close to that in parent submitochondrial particles. The succinate reduced enzyme exhibits ferredoxin-type iron-sulfur center EPR-signal (g = 1.94 species) and a semiquinone signal (g = 2.00). An oxidized preparation shows a symmetric signal centered around g = 2.01. An unusual dissociation of the enzyme in the absence of a detergent is described. When added to the assay mixture from a concentrated protein-detergent solution, the enzyme does not reduce Q2 being highly reactive towards ferricyanide ('low Km ferricyanide reactive site'; Vinogradov, A.D., Gavrikova, E.V. and Goloveshkina, V.G. (1975) Biochem. Biophys. Res. Commun. 65, 1264-1269). The ubiquinone reductase, not the ferricyanide reductase was observed when the enzyme was added to the assay mixture from the diluted protein-detergent solutions. Thus the dissociation of succinate dehydrogenase from the complex occurs in the absence of a detergent dependent on the concentration of the protein-detergent complex in the stock preparation where the samples for the assay are taken from. An active antimycin-sensitive succinate-cytochrome c reductase was reconstituted by admixing of the soluble succinate-ubiquinone reductase and the cytochrome b-c1 complex, i.e., from the complexes which both contain the ubiquinone reactivity conferring protein (QPs). Cytochrome c reductase was also reconstituted from the succinate-ubiquinone reductase and succinate-cytochrome c reductase containing inactivated succinate dehydrogenase. The reconstitution experiments suggest that there exists a specific protein-protein (or lipid) interaction between QPs and a certain component(s) of the b-c1 complex.
 ...
PMID:Studies on the succinate dehydrogenating system. Isolation and properties of the mitochondrial succinate-ubiquinone reductase. 299 19

A simple, rapid procedure suitable for large scale preparation of a lipid deficient cytochrome b6-f complex from spinach chloroplasts has been developed. The procedure involves solubilization with a mixture of sodium cholate and octylglucoside, ammonium sulfate fractionation and calcium phosphate column chromatography. The purified complex contains, in nanomoles per milligram protein, 20.6 cytochrome b, 10.8 cytochrome f and 54 phospholipids. The purified complex has little plastoquinol-cytochrome c reductase activity in the absence of added lipid. Full reductase activity was reconstituted by the addition of plastoquinone prior to the addition of lipid.
 ...
PMID:Preparation and reconstitution of a phospholipid deficient cytochrome b6-f complex from spinach chloroplasts. 299 23

Depletion of endogenous ubiquinone by pentane extraction of mitochondrial membranes lowered succinate-ferricyanide reductase activity, whereas quinone reincorporation restored the enzymatic activity as well as antimycin sensitivity. The oxidant-induced cytochrome b extrareduction, normally found upon ferricyanide pulse in intact mitochondria in the presence of antimycin, was lost in ubiquinone-depleted membranes, even if cytochrome c was added. Readdition of ubiquinone-2 restored the oxidant-induced extrareduction with an apparent half saturation at 1 mol/mol bc1 complex saturating at about 5 mol/mol. These findings demonstrate a requirement for the ubiquinone pool of the cytochrome b extrareduction. Since the initial rates of cytochrome b reoxidation upon ferricyanide addition, in the presence of antimycin, did not saturate by any ferricyanide concentration in ubiquinone-depleted mitochondria, a direct chemical reaction between ferricyanide and reduced cytochrome b was postulated. The fact that such direct reaction is much faster in ubiquinone-depleted mitochondria may explain the lower antimycin sensitivity of the succinate ferricyanide reductase activity after removal of endogenous ubiquinone.
 ...
PMID:Effect of ubiquinone extraction on the reaction of the mitochondrial bc1 complex with ferricyanide. 300 46


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