Redox poise

Fig. 3. A comparison of the Ni K-edge XAS spectra for redox poised samples of several hydrogenases (reprinted with permission from 74) copyright 1997, American Chemical Society). Bold hnes, T. roseopersicina hght hne, D. gigas dotted line, C. vinosum dashed line, D. desulfuricans ATCC 27774 dashed-dotted line, E. coli.

Fig. 4. EPR spectra of redox poised hydrogenase from T. roseopercisina. Theg values are indicated. (Reprinted with permission from (,64) copyright 1997, American Chemical Society).

Fig. 5. FTIR spectra of redox-poised D. gigas hydrogenase. (Reprinted with permission from (65) cop3Tight 1997, AmericEm ChemicEd Society). See Edso Table I.

Bacteria, fungi, and plants have a thioredoxin reductase system involving Se-containing thioredoxin reductase (EC 1.8.1.9), NADPH, and thioredoxin. Effecting the intercellular redox poise, this system interacts in selenium... 

Obviously the redox poise in biological systems is very important and the movement of selenium through this process has been investigated for denitrifiers such as Paracoccus denitrificans,159 a specialized selenate-respiring bacterium Thauera selenatis which used selenate as the sole electron acceptor,160,161 and phototrophic bacteria which produced different reduced forms of selenium when amended with either selenite or selenate and even added insoluble elemental Se.162 As noted above, Andreesen has commented on the importance of redox active selenocysteines135 and Jacob et al.136 note the importance of the thioredoxin system to redox poise. 

A comparison of the Ni K-edge X-ray absorption spectra for redox-poised samples of hydrogenases from different bacteria in the edge and XANES regions... 

A comparison of the filtered EXAFS data (1.0-2.6 A) for redox-poised samples of hydrogenases... 

Figure 7.20 A comparison of the filtered EXAFS data (1.0-2.6 A) for redox-poised samples of hydrogenases. Spectra are separated by redox level, with line types indicating different bacterial sources (see Figure 7.19 caption for linetype definitions). Reprinted with permission from Gu, et o/. (1996) and the American Chemical Society.

Appel, J. and Schulz, R. (1998) Hydrogen metabolism in organisms with oxygeneic photosynthesis Hydrogenases as important regulatory devices for a proper redox poising. J. Photobiochem. PhotobioL, 47, 1-11. 

Allen s theory of redox poise, and the evidence supporting it, are discussed in Chap. 3 of this volume. Here, I want to make a few general observations on necessity and workability. Each mitochondrion needs a genome because the speed of electron flow down the respiratory chains depends not just on supply and demand (concentration of NADH, 02, ADP and inorganic phosphate) but also on the number and redox state of respiratory complexes (Allen 1993,... 

Figure 4. First coordination sphere (backtransform window = 1.1-2.7 A) Fourier-filtered Ni K-edge EXAFS spectra from redox-poised Thiocapsa ro-...

In chromatophores light flash-induced reduction of the b cytochromes (e.g., in the presence of antimycin) is not associated with conservation of energy, as judged from the lack of an electrogenic spectral change in the carotenoids. It is the antimycin-sensitive reoxidation of cytochromes b (through site i ) that appears electrogenic in this sense (see Refs. 87, 276, 277). This contrasts to models (cf.. Fig. 3.9) of electron translocation by the b cytochromes, and the observations that the relative redox poise of the haems is distorted by Aif- [246,278]. However, the position of carotenoids may be such in the membrane that a local field between the b haems is not sensed until it is delocalised. Such a field could also be distorted by a bound SQ molecule. 

P-430) [61]. Later a second, different ESR signal (center B) could be observed only by illuminating at room, and not at cryogenic, temperature under suitable redox poise [62]. The attribution of these signals to the reduction of Fe-S centers comes from the speetral similarities with known isolated Fe-S proteins and from the... 

XAS and EPR redox titration of the Cys207— Ser mutant human sulfite oxidase. The Mo(v) EPR signal intensity is zero on the reductive half of the titration (open points) and climbs to 100% Mo(v) on the oxidative half-titration (filled points). The EXAFS Fourier transforms (Mo-S phase-corrected) of redox-poised samples are shown adjacent to the potentials above the redox titration and the structures derived from curve-fitting of the different oxidation states are shown above the transforms. The figure used the data of George et alf° replotted. 

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