A novel membrane-bound flavocytochrome c sulfide dehydrogenase from the colourless sulfur bacterium Thiobacillus sp. W5 |
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Authors: | J M Visser Govardus A H de Jong L A Robertson J Gijs Kuenen |
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Institution: | (1) Department of Microbiology and Enzymology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands Tel. +31-15-2782421; Fax +31-15-2782355 e-mail l.a.robertson@stm.tudelft.nl, NL |
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Abstract: | A novel membrane-bound sulfide-oxidizing enzyme was purified 102-fold from the neutrophilic, obligately chemolithoautotrophic
Thiobacillus sp. W5 by means of a six-step procedure. Spectral analysis revealed that the enzyme contains haem c and flavin. SDS-PAGE showed the presence of two types of subunit with molecular masses of 40 and 11 kDa. The smaller subunit
contains covalently bound haem c, as was shown by haem staining. A combination of spectral analysis and the pyridine haemochrome test indicated that the sulfide-oxidizing
heterodimer contains one molecule of haem c and one molecule of flavin. It appeared that the sulfide-oxidizing enzyme is a
member of a small class of redox proteins, the flavocytochromes c, and is structurally most related to the flavocytochrome c sulfide dehydrogenase of the green sulfur bacterium Chlorobium limicola. The pH optimum of the enzyme is 8.6. At pH 9, the V
max was 2.1 ± 0.1 μmol cytochrome c (mg protein)–1 min–1, and the K
m values for sulfide and cytochrome c were 1.7 ± 0.4 μM and 3.8 ± 0.8 μM, respectively. Cyanide inhibited the enzyme by the formation of an N-5 adduct with the
flavin moiety of the protein. On the basis of electron transfer stoichiometry, it seems likely that sulfur is the oxidation
product.
Received: 15 October 1996 / Accepted: 7 January 1997 |
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Keywords: | Thiobacillus sp W5 Sulfide oxidation Sulfur formation Flavocytochrome c Chlorobium limicola Chromatium vinosum Thiobacilli |
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