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  • 1
    ISSN: 1432-072X
    Keywords: Rhodobacter capsulatus ; Nitrate reduction ; Auxiliary electron transport ; Myxothiazol ; 2-n-heptyl-4-hydroxyquinoline-N-oxide ; Ubiquinone pool
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of various electron transport inhibitors upon the rates of reduction NO 3 - , dimethyl sulphoxide (DMSO) and N2O in anaerobic suspensions of Rhodobacter capsulatus have been studied. A new method for the determination of the rates of reduction of these auxiliary oxidants in intact cells is presented, based on the proportionality observed between the concentration of oxidant and the duration of the electrochromic carotenoid bandshift. For NO 3 - and N2O good agreement was found between rates of reduction determined using electrodes and those determined by the electrochromic method. Myxothiazol and antimycin A had no effect on the rates of reduction of NO 3 - and DMSO suggesting that the cytochrome b/c 1complex is not involved in electron transport to these oxidants. 2-n-heptyl-4-hydroxyquinoline-N-oxide (HOQNO) inhibited at two sites, one within the cytochrome b/c 1complex and the other on the nitrate reducing pathay, but had no effect on electron transport to N2O or DMSO. In both intact cells and cell free extracts, HOQNO had no effect on the nitrate dependent re-oxidation of reduced methylviologen (MVH2), a direct electron donor to nitrate reductase. Our data are consistent with a branch point for the auxiliary electron transport pathways at the level of the ubiquinone pool.
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  • 2
    ISSN: 1432-072X
    Keywords: Rhodobacter capsulatus ; Periplasmic enzymes ; Nitrate reductase ; Trimethylamine-N-oxide/dimethylsulphoxide/chlorate reductase ; Molybdenum cofactor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The periplasmic dissimilatory nitrate reductase from Rhodobacter capsulatus N22DNAR+ has been purified. It comprises a single type of polypeptide chain with subunit molecular weight 90,000 and does not contain heme. Chlorate is not an alternative substrate. A molybdenum cofactor, of the pterin type found in both nitrate reductases and molybdoenzymes from various sources, is present in nitrate reductase from R. capsulatus at an approximate stoichiometry of 1 molecule per polypeptide chain. This is the first report of the occurrence of the cofactor in a periplasmic enzyme. Trimethylamine-N-oxide reductase activity was fractionated by ion exchange chromatography of periplasmic proteins. The fractionated material was active towards dimethylsulphoxide, chlorate and methionine sulphoxide, but not nitrate. A catalytic polypeptide of molecular weight 46,000 was identified by staining for trimethylamine-N-oxide reductase activity after polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The same polypeptide also stained for dimethylsulphoxide reductase activity which indicates that trimethylamine-N-oxide and dimethylsulphoxide share a common reductase.
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  • 3
    ISSN: 1432-072X
    Keywords: Rhodobacter capsulatus ; Nuclear magnetic resonance assay ; Dimethyl sulphoxide ; Dimethyl sulphide ; Trimethylamine-N-oxide ; Trimethylamine ; Electron transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nuclear magnetic resonance is established as a sensitive and specific method for following the reduction of dimethylsulphoxide and trimethylamine-N-oxide by bacteria. Using this method it has been shown that cells of Rhodobacter capsulatus reduce both dimethylsulphoxide and trimethylamine-N-oxide at linear rates at all concentrations of these acceptors that can be conveniently detected during a continuous assay. The rate of reduction of trimethylamine-N-oxide was eightfold higher than the rate of dimethylsulphoxide reduction. An upper limit of approximately 0.1 mM may be placed upon the apparent K m value for each acceptor, but the value for dimethylsulphoxide is deduced to be lower than that for trimethylamine-N-oxide on the basis of the strong inhibitory effect of the former on the reduction of the latter. Reduction of trimethylamine-N-oxide by Rb. capsulatus was inhibited by illumination and by oxygen, but only the former effect was relieved following dissipation of the proton electrochemical gradient across the cytoplasmic membrane. Rotenone inhibited the reduction of trimethylamine-N-oxide whereas myxothiazol did not, consistent with a pathway of electrons to the reductase from NADH dehydrogenase that does not involve the cytochrome bc 1complex.
    Type of Medium: Electronic Resource
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