Carbon dioxide fixation process

Photogenerated cofactors can be employed to drive biocatalytic enzyme cascades including the photosynthetic carbon dioxide fixation process [184] (Figure 35). Photogenerated NADPH provides a two-electron relay for the insertion of CO2 into a-ketoglutaric acid (23) and pyruvic acid (21) in the presence of isocitrate dehydrogenase (IcitDH) and malic enzyme (MalE), respectively. In these photosystems, Ru(bpy)3 " acts as a photosensitizer, as a primary electron acceptor... 

Interestingly, the photoinduced regeneration system of NADPH has also been applied in photosynthetic carbon dioxide fixation processes [82]. Insertion of COj into a carbon backbone represents a two-electron fixation of carbon dioxide ... 

FUNCTION RUBISCO CATALYSES TWO REACTIONS THE CARBOXYLATION OF D-RIBULOSE 1,5-BISPHOSPHATE, THE PRIMARY EVENT IN PHOTOSYNTHETIC CARBON DIOXIDE FIXATION, AS WELL AS THE OXIDATIVE FRAGMENTATION OF THE PENTOSE SUBSTRATE IN THE PHOTORESPIRATION PROCESS. BOTH REACTIONS OCCUR SIMULTANEOUSLY AND IN COMPETITION AT THE SAME ACTIVE SITE. 

These are involved in a wide range of electron-transfer processes and in certain oxidation-reduction enzymes, whose function is central to such important processes as the nitrogen cycle, photosynthesis, electron transfer in mitochondria and carbon dioxide fixation. The iron-sulfur proteins display a wide range of redox potentials, from +350 mV in photosynthetic bacteria to —600 mV in chloroplasts. 

Starvation. The early reports that Hill inhibitors limited photosynthesis and that starch disappeared from treated plants, prompted some investigators to refer to these compounds as photosynthesis inhibitors. Photosynthesis is inhibited because ATP and NADFH are not available for carbon dioxide fixation. However, there is little evidence that the plants starve to death. If this were the only process affected, phytotoxic symptoms should resemble those that appear on plants kept in total darkness. Deficiency of photosynthate does limit new growth, but does not account for the morphological alterations that occur within a few hours after treatment. The mechanisms that lead to phytotoxicity appear to be considerably more complex than would result from limiting carbohydrate synthesis by suppression of carbon dioxide fixation (2). ... 

Autotrophic microorganisms synthesize organic substances from carbon dioxide through a process known as carbon dioxide fixation. They are important in nature because carbon dioxide fixation works as a precursor for the organic substrates that form the basis of the food chain for other organisms. Autotrophic bacteria include those that obtain their energy from light (photoautotrophs) and those that obtain it from the oxidation of chemical bonds (chemoau-totrophs). 

The photochemical carboxylation of pyruvic acid by this process is endergonic by about AG° = 11.5 kcal mol and represents a true uphill photosynthetic pathway. The carbon dioxide fixation product can then act as the source substrate for subsequent biocatalyzed transformations. For example, photogenerated malic acid can act as the source substrate for aspartic acid (Figure 35). In this case, malic acid is dehydrated by fumarase (Fum) and the intermediate fumaric acid is aminated in the presence of aspartase (Asp) to give aspartic acid. 

The lithoautotrophs have to form cellular materials from carbon dioxide. The process to change carbon dioxide into organic compounds is called fixation of carbon dioxide. On the basis of the knowledge to date, all algae and cyanobacteria, and many of the plants, fix carbon dioxide through the Calvin-Benson cycle (or reductive pentose phosphate cycle) (Bassham et al., 1954), while the plants of 20 families and 1200 species have been known to fix carbon dioxide through the Hatch-Slack pathway (or C4 dicarboxylate pathway) (Hatch et al., 1967). 

RuBP is the intermediate of the Calvin cycle onto which C02 is added in the process of carbon dioxide fixation. The reaction below -is catalyzed by the enzyme called 0 rubisco... 

The reactions of the Calvin cycle, which is the process of carbon dioxide fixation in plants (also known as the dark cycle), are listed below ... 

Several redox transformations that can be driven in such artificial photosynthetic systems are summarized in Table 1 and include photolysis of water, carbon dioxide fixation, and nitrogen fixation processes. The endoergicities of these transformations and the number of electrons involved in the reduction processes are also included in Table 1. It can be realized that the energy per electron required to drive the various transformations is available in visible-light quanta. It should be noted, however, that the overall... 

Furthermore, it can be seen that reduction of CO2 can lead to various Cj-fuel products, and that carbon dioxide fixation in aqueous media is accompanied by the competitive H2-evolution process. Thus the developed catalysts must exhibit selectivity toward the desired product and respective substrate. In addition to carbon dioxide and water, nitrogen-containing compounds can be used as substrates for the reduced photoproduct. Several reduction processes of nitrogen-containing substrates are summarized as follows ... 

Carbon dioxide fixation takes place in the stroma. The equation for the overall reaction, like all equations for photosynthetic processes, is deceptively simple. 

Kasiri S, Ulrich A, Prasad V Kinetic modeling and optimization of carbon dioxide fixation using microalgae cultivated in oil-sands process water, Chem EngSci 137 697—711,2015. 

Iron-sulfur proteins, Fe-S-proteins a group of proteins found in all organisms. They contain iron-sulfur centers (iron-sulfur clusters) and take part in electron transfer processes. They are involved In Hj metabolism, nitrogen and carbon dioxide fixation, oxidative and photosynthetic phosphorylation, mitochondrial hydroxylation and nitrite and sulfite reduction. The iron in the active centers is coordinated with the sulfur atoms of cysteine residues. In addition, all Fe-S-proteins except for Rubredoxins (see) contain the same number of labile or inorganic sulfur atoms as iron atoms, and both are covalently bound in iron-sulfur clusters. Since the iron is not bound in a porphyrin ring, this group of proteins is included in the Non-... 

Photosynthetic carbon dioxide fixation into oi-keto acids has recently been found to be the major pathway in some organisms. The process appears to be essentially a reversal of the mitochondrial oxidative decarboxylation processs. The photoreduction is mediated through a ferredoxin system similar to the photosynthetic nicotinamide coenzyme reductase. The involvement of lipoic add has not yet been shown, but it would be expected and could provide the long-sought role of lipoate in photosynthesis. 

The early work in photosynthesis was based on the assumption that carbon dioxide fixation was a process unique in green plants, and studies were made on the effect of various external factors such as light intensity, light quahty, carbon dioxide concentration, and temperature. Certain internal factors were also recognized as affecting photosynthesis. Many fundamental studies on photosynthesis were concerned with the chemistry of the chlorophyll molecule. Enzymes were studied, and attempts were made to carry out cell-free photosynthesis by conventional biochemical techniques. While these studies contributed a great deal of information regarding the photosynthetic reaction, they did little to elucidate the mechanism of the process. 

The methanol molecule is smaller than carbon dioxide and penetrates most plant tissues quickly for rapid metabolism. As a plant source of carbon, methanol is a liquid concentrate 1 cc methanol provides the equivalent fixed-carbon substrate of over 2,000,000 cc of ambient air. Methanol absorbed by foliage is metabolized to carbon dioxide, amino acids, sugars, and other structural components. Two major paths of methanol metabolism are the internal production of carbon dioxide that is then utilized in photosynthesis and the incorporation of methanol as a fixed source of carbon. Briefly stated in field terms, methanol treatments are a means of placing carbon directly into the foliage. Hi li t intensity is necessary to drive photosynthesis at the rates necessary to process the high internal levels of carbon dioxide presented by methanol. Serine formation and carbon dioxide fixation by photosynthesis may lead to the production of su. Increases of su concentration in the presence of moisture lead to increased turgidity. 

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