Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.2 (NQO1)
 6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Membranes of the green sulfur bacterium, Chlorobium limicola f. thiosulfatophilum, catalyze the reduction of externally added isoprenoid quinones by sulfide. This activity is highly sensitive to stigmatellin and aurachins. It is also inhibited by 2-n-nonyl-4-hydroxyquinoline-N-oxide, antimycin, myxothiazol and cyanide. It is concluded that in sulfide oxidizing bacteria like Chlorobium, sulfide oxidation involves a sulfide-quinone reductase (SQR) similar to the one found in Oscilatoria limnetica [Arieli, B., Padan, E. and Shahak, Y. (1991) J. Biol. Chem. 266, 104-111].
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PMID:Sulfide quinone reductase (SQR) activity in Chlorobium. 154 83

Sulfide-dependent partial electron-transport reactions were studied in thylakoids isolated from cells of the cyanobacterium Oscillatoria limnetica, which had been induced to perform sulfide-driven anoxygenic photosynthesis. It was found that these thylakoids have the capacity to catalyze electron transfer, from sulfide to externally added quinones, in the dark. Assay conditions were developed to measure the reaction either as quinone-dependent sulfide oxidation (colorimetrically) or as sulfide-dependent quinone reduction (by UV dual-wavelength spectrophotometry). The main features of this reaction are as follows. (i) It is exclusively catalyzed by thylakoids of sulfide-induced cells. Noninduced thylakoids lack this reaction. (ii) Plastoquinone-1 or -2 are equally good substrates. Ubiquinone-1 and duroquinone yield somewhat slower rates. (iii) The apparent Km for plastoquinone-1 was 32 microM and for sulfide about 4 microM. Maximal rates (at 25 degrees C) were about 75 mumol of quinone reduced per mg of chlorophyll.h. (iv) The reaction was not affected by extensive washes of the membranes. (v) Unlike sulfide-dependent NADP photoreduction activity of these thylakoids, which is sensitive to all the specific inhibitors of the cytochrome b6f complex, the new dark reaction exhibited differential sensitivity to these inhibitors. 2-n-Nonyl-4-hydroxyquinoline-N-oxide was the most potent inhibitor of both light and dark reactions, working at submicromolar concentrations. 5-n-Undecyl-6-hydroxy-4,7-dioxobenzothiazole also inhibited the two reactions to a similar extent, but at 10 times higher concentrations than 2-n-nonyl-4-hydroxyquinoline-N-oxide. 2,5-Dibromo-3-methyl-6-isopropyl-p-benzoquinone, 2-iodo-6-isopropyl-3-methyl-2',4,4'-trinitrodiphenyl ether, and stigmatellin had no effect on the dark reaction at concentrations sufficient to fully inhibit the light reaction from sulfide. We propose that the sulfide-induced factor which enables the use of sulfide as the electron donor for anoxygenic photosynthesis in Oscillatria limnetica is a membrane-bound sulfide-quinone reductase. Its site of interaction is suggested to be either the cytochrome b6 (at the Qc quinone binding site or the bH site) or the plastoquinone pool. The analogy to other anoxygenic photosynthetic systems is discussed.
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PMID:Sulfide-induced sulfide-quinone reductase activity in thylakoids of Oscillatoria limnetica. 189 23

The gene encoding sulfide-quinone reductase (SQR; E.C.1.8.5.'), the enzyme catalyzing the first step of anoxygenic photosynthesis in the filamentous cyanobacterium Oscillatoria limnetica, was cloned by use of amino acid sequences of tryptic peptides as well as sequences conserved in the Rhodobacter capsulatus SQR and in an open reading frame found in the genome of Aquifex aeolicus. SQR activity was also detected in the unicellular cyanobacterium Aphanothece halophytica following sulfide induction, with a V(max) of 180 micromol of plastoquinone-1 (PQ-1) reduced/mg of chlorophyll/h and apparent K(m) values of 20 and 40 microM for sulfide and quinone, respectively. Based on the conserved sequences, the gene encoding A. halophytica SQR was also cloned. The SQR polypeptides deduced from the two cyanobacterial genes consist of 436 amino acids for O. limnetica SQR and 437 amino acids for A. halophytica SQR and show 58% identity and 74% similarity. The calculated molecular mass is about 48 kDa for both proteins; the theoretical isoelectric points are 7.7 and 5.6 and the net charges at a neutral pH are 0 and -14 for O. limnetica SQR and A. halophytica SQR, respectively. A search of databases showed SQR homologs in the genomes of the cyanobacterium Anabaena PCC7120 as well as the chemolithotrophic bacteria Shewanella putrefaciens and Thiobacillus ferrooxidans. All SQR enzymes contain characteristic flavin adenine dinucleotide binding fingerprints. The cyanobacterial proteins were expressed in Escherichia coli under the control of the T7 promoter. Membranes isolated from E. coli cells expressing A. halophytica SQR performed sulfide-dependent PQ-1 reduction that was sensitive to the quinone analog inhibitor 2n-nonyl-4-hydroxyquinoline-N-oxide. The wide distribution of SQR genes emphasizes the important role of SQR in the sulfur cycle in nature.
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PMID:Cyanobacterial sulfide-quinone reductase: cloning and heterologous expression. 1085 62

The Thermus thermophilus succinate:quinone reductase (SQR), serving as the respiratory complex II, has been homologously produced under the control of a constitutive promoter and subsequently purified. The detailed biochemical characterization of the resulting wild type (wt-rcII) and His-tagged (rcII-His(8)-SdhB and rcII-SdhB-His(6)) complex II variants showed the same properties as the native enzyme with respect to the subunit composition, redox cofactor content and sensitivity to the inhibitors malonate, oxaloacetate, 3-nitropropionic acid and nonyl-4-hydroxyquinoline-N-oxide (NQNO). The position of the His-tag determined whether the enzyme retained its native trimeric conformation or whether it was present in a monomeric form. Only the trimer exhibited positive cooperativity at high temperatures. The EPR signal of the [2Fe-2S] cluster was sensitive to the presence of substrate and showed an increased rhombicity in the presence of succinate in the native and in all recombinant forms of the enzyme. The detailed analysis of the shape of this signal as a function of pH, substrate concentration and in the presence of various inhibitors and quinones is presented, leading to a model for the molecular mechanism that underlies the influence of succinate on the rhombicity of the EPR signal of the proximal iron-sulfur cluster.
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PMID:Atypical features of Thermus thermophilus succinate:quinone reductase. 2330 53