hexacyanoferrate-iii and quinone

Escherichia coli and many other Gram-negative pathogenic bacteria protect themselves from the toxic effects of electrophilic compounds by using a potassium efflux system (Kef). Potassium efflux is coupled to the influx of protons, which lowers the internal pH and results in immediate protection. The activity of the Kef system is subject to complex regulation by glutathione and its S conjugates. Full activation of KefC requires a soluble ancillary protein, KefF. This protein has structural similarities to oxidoreductases, including human quinone reductases 1 and 2. Here, we show that KefF has enzymatic activity as an oxidoreductase, in addition to its role as the KefC activator. It accepts NADH and NADPH as electron donors and quinones and ferricyanide (in addition to other compounds) as acceptors. However, typical electrophilic activators of the Kef system, e.g., N-ethyl maleimide, are not substrates. If the enzymatic activity is disrupted by site-directed mutagenesis while retaining structural integrity, KefF is still able to activate the Kef system, showing that the role as an activator is independent of the enzyme activity. Potassium efflux assays show that electrophilic quinones are able to activate the Kef system by forming S conjugates with glutathione. Therefore, it appears that the enzymatic activity of KefF diminishes the redox toxicity of quinones, in parallel with the protection afforded by activation of the Kef system.

Topics: Benzoquinones; Escherichia coli; Escherichia coli Proteins; Ferricyanides; Humans; Mutagenesis, Site-Directed; NAD; NAD(P)H Dehydrogenase (Quinone); NADP; Oxidoreductases; Potassium; Potassium Channels; Protein Subunits

Destruction of guard cell nuclei in epidermis isolated from leaves of pea, maize, sunflower, and haricot bean, as well as destruction of cell nuclei in leaves of the aquatic plants waterweed and eelgrass were induced by cyanide. Destruction of nuclei was strengthened by illumination, prevented by the antioxidant alpha-tocopherol and an electron acceptor N,N,N ,N -tetramethyl-p-phenylenediamine, and removed by quinacrine. Photosynthetic O2 evolution by the leaf slices of a C3 plant (pea), or a C4 plant (maize) was inhibited by CN- inactivating ribulose-1,5-bisphosphate carboxylase, and was renewed by subsequent addition of the electron acceptor p-benzoquinone.

Topics: alpha-Tocopherol; Antioxidants; Apoptosis; Benzoquinones; Cell Nucleus; Cyanides; Diuron; Ferricyanides; Fluorometry; Helianthus; Hydrocharitaceae; Oxygen; Phaseolus; Pisum sativum; Plant Epidermis; Plant Leaves; Potassium Cyanide; Quinacrine; Tetramethylphenylenediamine; Zea mays

Flash-induced redox changes of b-type and c-type cytochromes have been studied in chromatophores from the aerobic photosynthetic bacterium Roseobacter denitrificans under redox-controlled conditions. The flash-oxidized primary donor P+ of the reaction center (RC) is rapidly re-reduced by heme H1 (Em,7 = 290 mV), heme H2 (Em,7 = 240 mV) or low-potential hemes L1/L2 (Em,7 = 90 mV) of the RC-bound tetraheme, depending on their redox state before photoexcitation. By titrating the extent of flash-induced low-potential heme oxidation, a midpoint potential equal to -50 mV has been determined for the primary quinone acceptor QA. Only the photo-oxidized heme H2 is re-reduced in tens of milliseconds, in a reaction sensitive to inhibitors of the bc1 complex, leading to the concomitant oxidation of a cytochrome c spectrally distinct from the RC-bound hemes. This reaction involves cytochrome c551 in a diffusional process. Participation of the bc1 complex in a cyclic electron transfer chain has been demonstrated by detection of flash-induced reduction of cytochrome b561, stimulated by antimycin and inhibited by myxothiazol. Cytochrome b561, reduced upon flash excitation, is re-oxidized slowly even in the absence of antimycin. The rate of reduction of cytochrome b561 in the presence of antimycin increases upon lowering the ambient redox potential, most likely reflecting the progressive prereduction of the ubiquinone pool. Chromatophores contain approximately 20 ubiquinone-10 molecules per RC. At the optimal redox poise, approximately 0.3 cytochrome b molecules per RC are reduced following flash excitation. Cytochrome b reduction titrates out at Eh < 100 mV, when low-potential heme(s) rapidly re-reduce P+ preventing cyclic electron transfer. Results can be rationalized in the framework of a Q-cycle-type model.

Topics: Antimycin A; Bacteria; Bacterial Physiological Phenomena; Benzoquinones; Cytochrome b Group; Cytochrome c Group; Electron Transport Complex III; Electrons; Enzyme Inhibitors; Ferricyanides; Kinetics; Light; Methacrylates; Naphthoquinones; Oxidation-Reduction; Phenylenediamines; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Proteobacteria; Thiazoles; Time Factors; Titrimetry

Quinones which are produced during the mineralization of lignin and xenobiotics by the white rot fungus Phanerochaete chrysosporium were reduced by a plasma membrane redox system of the fungus. Both intracellular enzymes and the plasma membrane redox system were able to reduce 1,4-benzoquinone. However, no quinone reductase activity was observed with the extracellular culture fluid. The intracellular reductase activity had a pH optimum between 6.0 and 7.0 and a Km of 150 microM. Reduction of 1,4-benzoquinone by the plasma membrane redox system had a pH optimum between 7.5 and 8.5 and exhibited saturation kinetics (Km = 11 microM, Vmax = 16 nmol/min/mg mycelia dry weight). Ferricyanide totally inhibited the quinone reduction until the ferricyanide was completely reduced by the membrane. Radicals (chlorpromazine and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS)) that can be generated by the lignin peroxidases were also reduced by the plasma membrane redox system. Reduction of the ABTS cation radical also totally inhibited quinone reduction until the radical was completely reduced. Finally, quinone reduction rates were identical after the reduction of ferricyanide, ABTS cation radical, or quinone, suggesting that the plasma membrane redox system may actually protect the fungus from oxidative damage from free radicals generated by the lignin degrading system.

Topics: Basidiomycota; Benzoquinones; Benzothiazoles; Biodegradation, Environmental; Cell Membrane; Chlorpromazine; Ferricyanides; Free Radicals; Hydrogen-Ion Concentration; Kinetics; Lignin; Minerals; Oxidation-Reduction; Sulfonic Acids

Topics: Benzoquinones; Carbon Dioxide; Cyanides; Edible Grain; Ferricyanides; Humans; Photosynthesis; Plant Structures; Quinones

Topics: Benzoquinones; Chlorella; Eukaryota; Ferricyanides; Ferrocyanides; Photosynthesis; Quinones

Topics: Benzoquinones; Chlorella; Cyanides; Eukaryota; Ferricyanides; Humans; Oxidation-Reduction; Quinones