The periplasmic nitrate reductase of Rhodobacter capsulatus; purification,characterisation and distinction from a single reductase for trimethylamine-N-oxide,dimethylsulphoxide and chlorate |
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Authors: | A G McEwan H G Wetzstein O Meyer J B Jackson S J Ferguson |
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Institution: | (1) Department of Biochemistry, University of Birmingham, P. O. Box 363, B15 2TT Birmingham, UK;(2) Institut für Mikrobiologie der Universität Göttingen, D-3400 Göttingen, Federal Republic of Germany;(3) Present address: Department of Microbiology, University of Illinois, 61801 Urbana, IL, USA;(4) Present address: Bayer AG, D-5090 Leverkusen, Federal Republic of Germany;(5) Present address: Institut für Pflanzenphysiologie und Mikrobiologie, Freie Universität Berlin, Königin-Luise-Str. 12-16a, D-1000 Berlin 33;(6) Present address: Department of Biochemistry, University of Oxford, South Parks Road, OX1 3QU Oxford, UK |
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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.Abbreviations DMSO
dimethylsulphoxide
- LDS
lithium dodecyl sulphate
- MVH
reduced methylviologen
- PAGE
polyacrylamide gel electrophoresis
- SDS
sodium dodecyl sulphate
- TMAO
trimethylamine-N-oxide |
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Keywords: | Rhodobacter capsulatus Periplasmic enzymes Nitrate reductase Trimethylamine-N-oxide/dimethylsulphoxide/chlorate reductase Molybdenum cofactor |
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