Sulfide-quinone reductase activity in membranes of the chemotrophic bacterium Paracoccus denitrificans GB17

• Published in: Archives of microbiology 1998, Vol.170 (5), p.353-360
• Main Authors: SCHÜTZ, M, KLUGHAMMER, C, GRIESBECK, C, QUENTMEIER, A, FRIEDRICH, C. G, HAUSKA, G
• Format: Article
• Language: English
• Subjects: Bacteriology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Metabolism. Enzymes; Microbiology
• ISSN: 0302-8933; 1432-072X
• DOI: 10.1007/s002030050653

Reduction of exogenous ubiquinone and of cytochromes by sulfide in membranes of the chemotrophic bacterium Paracoccus denitrificans GB17 was studied. For sulfide-ubiquinone reductase activity, Km values of 26 plus or minus 4 and 3.1 plus or minus 0.6 mM were determined from titrations with sulfide and decyl-ubiquinone, respectively. A maximal rate of up to 0.3 mmol decyl-ubiquinone reduced (mg protein)-1 min-1 was estimated. The reaction was sensitive to quinone-analogous inhibitors, but insensitive to cyanide. Reduction of cytochromes by sulfide was monitored with an LED-array spectrophotometer. Under oxic conditions, reduction rates and extents of reduction were lower than those under anoxic conditions. Reoxidation of cytochromes was oxygen-dependent and cyanide-sensitive. The multiphasic behavior of transient reduction of cytochrome b with limiting amounts of sulfide reflects that sulfide, in addition to acting as an electron donor, is a slowly binding inhibitor of cytochrome c oxidase. The initial peak of cytochrome b reduction is dependent on electron flow to an oxidant, either oxygen or ferricyanide, and is stimulated by antimycin A. This oxidant-induced reduction of cytochrome b suggests that electron transport from sulfide in P. denitrificans GB17 employs the cytochrome bc1 complex via the quinone pool.