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  • 1
    Electronic Resource
    Electronic Resource
    Sulfide-quinone reductase activity in membranes of the chemotrophic bacterium Paracoccus denitrificans GB17 (1998)
    Springer
    Archives of microbiology 170 (1998), S. 353-360 
    Details
    ISSN: 1432-072X
    Keywords: Key wordsParacoccus denitrificans ; Sulfide ; oxidation ; Sulfide-quinone reductase ; Cytochrome ; bc complex ; Flavocytochrome c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 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, K m values of 26 ± 4 and 3.1 ± 0.6 μM were determined from titrations with sulfide and decyl-ubiquinone, respectively. A maximal rate of up to 0.3 μmol 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 bc 1 complex via the quinone pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050653
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  • 2
    Electronic Resource
    Electronic Resource
    An improved method, using saturating light pulses, for the determination of photosystem I quantum yield via P700+-absorbance changes at 830 nm (1994)
    Springer
    Planta 192 (1994), S. 261-268 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Light absorbance (830 nm) ; P700 ; Photosynthesis ; Quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An improved method is introduced for the determination of the quantum yield of photosystem I. The new method employs saturating light pulses with steep rise characteristics to distinguish, in a given physiological state, centers with an open acceptor side from centers with a reduced acceptor side. The latter do not contribute to PSI quantum yield (ΦI). Oxidation of P700 is measured by a rapid modulation technique using the absorbance change around 830 nm. The quantum yield ΦI is calculated from the amplitude of the rapid phase of absorbance change (ΔA; 830 nm) upon application of a saturation pulse in a given state, divided by the maximal ΔA (830 nm) which is induced by a saturation pulse with far-red background illumination. Using this technique, ΦI can be determined even under conditions of acceptor-side limitation, as for example in the course of a dark-light induction period or after elimination of CO2 from the gas stream. Thus determined ΦI values display a close-to-linear relationship with those for the quantum yield of PSII (ΦII) calculated from chlorophyll fluorescence parameters. It is concluded that the proposed method may provide new information on the activity of the PSI acceptor side and thus help to separate the effects of acceptorside limitation from those of cyclic PSI, whenever a non-linear relationship between ΦII and the P700-reduction level is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01089043
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  • 3
    Electronic Resource
    Electronic Resource
    An improved method, using saturating light pulses, for the determination of photosystem I quantum yield via P700+-absorbance changes at 830 nm (1994)
    Springer
    Planta 192 (1994), S. 261-268 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Light absorbance (830 nm) ; P700 ; Photosynthesis ; Quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An improved method is introduced for the determination of the quantum yield of photosystem I. The new method employs saturating light pulses with steep rise characteristics to distinguish, in a given physiological state, centers with an open acceptor side from centers with a reduced acceptor side. The latter do not contribute to PSI quantum yield (ΦI). Oxidation of P700 is measured by a rapid modulation technique using the absorbance change around 830 nm. The quantum yield ΦI is calculated from the amplitude of the rapid phase of absorbance change (ΔA; 830 nm) upon application of a saturation pulse in a given state, divided by the maximal ΔA (830 nm) which is induced by a saturation pulse with far-red background illumination. Using this technique, ΦI can be determined even under conditions of acceptor-side limitation, as for example in the course of a dark-light induction period or after elimination of CO2 from the gas stream. Thus determined ΦI values display a close-to-linear relationship with those for the quantum yield of PSII (ΦII) calculated from chlorophyll fluorescence parameters. It is concluded that the proposed method may provide new information on the activity of the PSI acceptor side and thus help to separate the effects of acceptorside limitation from those of cyclic PSI, whenever a non-linear relationship between ΦII and the P700-reduction level is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194461
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  • 4
    Electronic Resource
    Electronic Resource
    LED array spectrophotometer for measurement of time resolved difference spectra in the 530–600 nm wavelength region (1990)
    Springer
    Photosynthesis research 25 (1990), S. 317-327 
    Details
    ISSN: 1573-5079
    Keywords: LED-Array Spectrophotometer ; difference spectroscopy ; time resolved spectra ; photosynthesis ; cytochrome b/f complex ; cytochrome b 559 ; heat-stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A new type of computer controlled spectrophotometer is described which is based on an array of independent, monochromatic pulsed light sources consisting of light emitting diodes (LED) equipped with narrow band interference filters. The LEDs are sequentially pulsed at a high repetition rate. The absorbance information at specific wavelengths is sampled in the μs-time range, using a computer-controlled, highly selective technique of synchronous amplification. A first prototype of this LED Array Spectrophotometer allows simultaneous recording of kinetic changes at 16 different wavelengths in the range from 530 to 600 nm, with a time resolution of 1 ms/point. Special features of the new type of spectrophotometer are: Weak integrated measuring light intensity, high signal/noise ratio even with scattering samples like intact leaves, active baseline adjustment by LED current regulation, computer control of system operation and data analysis. To deconvolute the complex absorbance changes in the cytochrome α-band region, ‘standard spectra’ of the major components are stored in computer memory and used for curve fitting of difference spectra and kinetic changes. As an example of application, the light-induced absorbance changes in a heat-pretreated spinach leaf are analysed. The system effectively separates specific absorbance changes of C550, cyt f, cyt b 559 and cyt b 563 from a large background of non-specific changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00033173
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  • 5
    Electronic Resource
    Electronic Resource
    Inhibition of cytochrome b563-oxidation by triorganotins in spinach chloroplasts (1998)
    Springer
    Photosynthesis research 56 (1998), S. 117-130 
    Details
    ISSN: 1573-5079
    Keywords: cytochrome bf complex ; proton transport ; Q-cycle ; triphenyltin chloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The triorganotin compounds triphenyltin chloride and tributyltin chloride have been known as inhibitors of the transmembrane proton channel forming F0-domain of ATPases at micromolar concentrations. We show that these compounds at higher concentrations (10–100 µM) also inhibit uncoupled electron transport in chloroplasts within the low potential chain of the cytochrome bf complex. They cause high levels of transiently reduced cytochrome b563 as they decelerate the reoxidation process in flash illuminated chloroplasts. At the same time they slow down the flash induced slow electrogenic step generated at the cytochrome bf complex. The inhibitory effect of triphenyltin chloride on cytochrome b563 turnover in chloroplasts is comparable to that of the Qn-inhibitor MOA-stilbene, with even less side effects on the high potential chain. Studies on the isolated bf complex suggest different binding sites for triorganotins and the quinone analogue type Qn-inhibitors. The results are interpreted within the framework of the modified Q-cycle model by a putative organotin sensitive proton translocating site which enables proton transfer from the outer aqueous face of the membrane to the hydrophobic quinone reduction site within the complex. Hence, cytochrome b563 oxidation and plastoquinone reduction may be inhibited as a consequence of proton transfer being suppressed by triorganotins. In analogy, the previously described inhibitory effect of Val/K+ at the n-side of the cytochrome bf complex [Klughammer and Schreiber (1993) FEBS 336: 491–495] may be rationalised by binding of the cyclic depsipeptide at the entrance of the proton path to the Qn-site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005998729041
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  • 6
    Electronic Resource
    Electronic Resource
    Sulfide-quinone and sulfide-cytochrome reduction in Rhodobacter capsulatus (1994)
    Springer
    Photosynthesis research 39 (1994), S. 175-181 
    Details
    ISSN: 1573-5079
    Keywords: sulfide-quinone reductase (SQR) ; Oselllatoria limnetiea ; Chlorobium limicola ; electron transport ; LED array spectrophotometer ; anoxygenic photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The reduction by sulfide of exogenous ubiquinone is compared to the reduction of cytochromes in chromatophores of Rhodobacter capsulatus. From titrations with sulfide values for Vmax of 300 and 10 μmoles reduced/mg bacteriochlorophyll a·h, and for Km of 5 and 3 μM were estimated, for decyl-ubiquinone-and cytochrome c-reduction, respectively. Both reactions are sensitive to KCN, as has been found for sulfide-quinone reductase (SQR) in Oscillatoria limnetica, which is a flavoprotein. Effects of inhibitors interfering with quinone binding sites suggest that at least part of the electron transport from sulfide in R. capsulatus employs the cytochrome bc 1-complex via the ubiquinone pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029384
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  • 7
    Electronic Resource
    Electronic Resource
    Reduction of cytochromes with menaquinol and sulfide in membranes from green sulfur bacteria (1995)
    Springer
    Photosynthesis research 43 (1995), S. 27-34 
    Details
    ISSN: 1573-5079
    Keywords: sulfide-quinone reductase (SQR) ; electron transport ; Chlorobium ; oxidant-induced reduction of cytochrome b ; cytochrome bc-complex ; menaquinone ; antimycin ; stigmatellin ; NQNO ; anoxygenic photosynthesis ; LED array spectrophotometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Reduction of cytochromes in chlorosome-free membranes of Chlorobia was studied anaerobically, with an LED array spectrophotometer. For Chlorobium tepidum these membranes contained 0.2 moles cytochrome per mole of bacteriochlorophyll a. The observed change upon complete reduction of oxidized membranes with dithionite could be satisfactorily fitted with three cytochrome components having absorption peaks at 553 (cyt c), 558 and 563 nm (cyt b), in relative amounts of 5:1:2. About 20% of total cytochrome 553 were reducible by ascorbate. Menaquinol reduced all of the 553-component, and this reduction was sensitive to stigmatellin, NQNO and antimycin A. The reduction was insensitive to KCN. However, it was transient at low concentrations of menaquinol in the absence of KCN, but permanent in its presence, demonstrating that electron transport into an oxidation pool was blocked. The 563-component was only slightly reduced by menaquinol unless NQNO or antimycin were present. The stimulation of cytochrome 563-reduction by these inhibitors was more pronounced in the presence of ferricyanide. This phenomenon reflects ‘oxidant-induced reduction’ of cytochrome b and demonstrates that a Q-cycle is operative in Chlorobia. Also, sulfide fully reduced cytochrome 553, but more slowly than menaquinol. KCN inhibited in this case, as did stigmatellin, NQNO and antimycin A. NQNO was a better inhibitor than antimycin A. Cytochrome 563 again was hardly reduced unless antimycin A was added. The effect was more difficult to observe with NQNO. This supports the conclusion that sulfide oxidation proceeds via the quinone pool and the cytochrome bc-complex in green sulfur bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029459
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