Redox mediators photosynthesis

Redox mediators provide an alternative to dissolved oxygen measurements for monitoring of respiration or photosynthesis. The mechanism is based on the reducing activity of metabolising biological whole cells ... 

A Z-scheme system mimicking the plant photosynthesis model developed with Pt-loaded Ti02 for HER and rutile Ti02 for OER. A IO3 /I shuttle was used as redox mediator. 330... 

Redox-mediated reactions are very common in biochemistry. More specifically, photo-induced redox-mediated reactions form the basis of photosynthesis in nature. 

Porphyrins are polyheterocyclic constituents of hemoglobin and myoglobin, the molecules that transport molecular oxygen in living systems (Section 26-8), of the cytochromes, which also play central roles in biological redox processes (Section 22-9), and of chlorophyll (Real Life 24-1), which mediates photosynthesis in all green plants. 

Fig. 3.2a Electron transport in (natural) photosynthesis. P = chlorophyll that acts as a light sensitizer, from which a photogenerated electron travels to Q = Plastquinone that in combination with CO2 forms a carbohydrate. The photo-ejected electron from Peso is replenished by taking one from the Mn cluster through the redox active tyrosine linkage (or mediator), which in turn extracts an electron from water.

Of course, the microbially mediated aquatic redox couples must be interrelated to the proper intracellular redox couples. For examples, the NADP system, ubiquitous in living organisms and believed to play a major role in electron transport during photosynthesis, exhibits pe (W) = -1-5.5. Moreover, various ferredoxins, now widely considered to be the primary electron receptors from excited chlorophylls, show pe°(W) values in the range —7.0 to —7.5 (Table 8.6b). The coincidence of this range with the pe°(W) value for conversion of CO2 to glucose is suggestive. 

Acid atmospheric deposition causes acidification of waters and soils if the neutralization of the acids by weathering is too slow. Biologically mediated redox processes are important in affecting the H balance. Among the redox processes that have a major impact on H" production and consumption are the synthesis and mineralization of biomass. Any uncoupling of linkages between photosynthesis and respiration affects acidity and alkalinity in terrestrial and aquatic ecosystems (Table 15.1). 

A.QUATIC oxidation-reduction (redox) processes control the distribution of many major and minor elements in natural environments (1). Equilibrium redox calculations can be used to indicate the boundary conditions toward which a natural system must be proceeding. Real systems are frequently far from equilibrium because photosynthesis traps the energy of the sun in the form of energy-rich chemical bonds and thus creates nonequilibrium chemical species. The return to equilibrium (even when mediated by bacteria)... 

Vectorial charge transfer and a molecular recognition at the interface between two dielectric media are important stages in many bioelectrochemical processes such as those mediated by energy-transducing membranes [1-4], Many biochemical redox reactions take place at aqueous medium/membrane interfaces and some of them are multielectron processes. About 90% of the oxygen consumed on Earth is reduced in a four-electron reaction catalyzed by cytochrome c oxidase. Multielectron reactions take place in photosynthesis, which is the most important process on earth [5-10]. Life on Earth began as photosynthesis. 

ACC regulation in cells is poorly understood, but redox control and phosphorylation are probably key factors. In pea, activation was found to be mediated through reduction of a disulfide bond between the a-CT and the j8-CT subunits [19]. Plastid ACC is likely to be subject to redox regulation similar to that of several key enzymes of photosynthesis. 

Fig. 3. Scheme of photoelectron transport in photosynthesis. The path of photoelectron flow associated with noncyclic photophosphorylation through the two postulated light reactions mediated by Pigment Systems 1 and 2 is indicated by the heavy lines. Redox potentials of electron-carrying cofactors along this path is indicated by scale on the left. Further explanation in text. 

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