The seeds of these mutants could germinate only at high CO 2 concentrations, although they were much worse developed as compared to WT plants J. Moroney, personal communication. CA protects the cells from H 2 O 2 -induced apoptosis [ 92 ]. It is known that among various chloroplast signals H 2 O 2 plays a major role in various signaling pathways under stress conditions [ 93 , 94 ].
An essential factor to implement the retrograde signal the signal from the organelle to the nucleus is the ability of H 2 O 2 to diffuse over long distances from the place of formation to the place of signaling.
Earlier, we demonstrated that H 2 O 2 that was produced inside chloroplasts diffused from a chloroplast to cytoplasm through chloroplast envelope membranes and the amount of H 2 O 2 outside the chloroplasts increased under the conditions of ascorbate peroxidase inhibition [ 95 ].
Using acetazolamide AZA , which is known as CA inhibitor, as a non-specific aquaporin inhibitor, we have shown that aquaporins facilitate the diffusion of H 2 O 2 molecules through the chloroplast membrane [ 16 ]. AZA was established to be an efficient inhibitor of aquaporins through interacting with the guanidyl group of Arg, backbone carbonyl of Gly, carboxyl of Asp, Ser, His, Ile and Asn of aquaporins [ 96 , 97 , 98 ].
Taking into consideration that AZA also inhibits the activity of CA, we cannot exclude that inhibition of H 2 O 2 diffusion through the envelope membrane in the presence of AZA was the only result of blocking of the aquaporins.
This inhibition could also result from inhibiting the envelope CA, especially if this CA is attached to aquaporins in the envelope. If this is the case, the inhibitory effect of AZA on the H 2 O 2 diffusion could be a consequence of AZA binding to envelope CA, leading to the conformational changes of CA with subsequent conformational changes of aquaporin proteins and therefore blocking the envelope aquaporins.
Thus, the data in [ 16 ] can represent the evidence of the joint functioning of the envelope CA with aquaporins in diffusing hydrogen peroxide through the chloroplast envelope. One of them is that CA is involved in the cascades of mitogen-activated protein kinases MAPKs , which are serine-threonine kinases mediating intracellular signaling through changes in the redox state of their cysteine residues. It was quantified that the amount of water in chloroplast stroma and thylakoid lumen was much lower than it is enough to perform photosynthetic water oxidation per day.
Therefore, the existence of aquaporins in the thylakoid membrane was also suggested [ ]. This question is still under debate, some researches have detected some forms of TIPs in the thylakoid membranes of Arabidopsis thaliana [ , ]. However, there is still little direct experimental evidence demonstrating the existence of aquaporins in thylakoid membranes and this question needs to be clarified in the future.
C3 higher plants are believed to lack any mechanisms of CO 2 concentrating. Under the illumination pH value of the chloroplast stroma, where Rubisco is located in higher plant cells, increases up to 7. This effect can be considered as inorganic carbon concentrating. For higher plants, especially when they grow under stress conditions, such as high light or high temperature, Zabaleta et al. At the same time, a large amount of CO 2 is released in mitochondria due to the reactions of both the tricarboxylic acid cycle and photorespiration.
The authors supposed that CO 2 from mitochondria can be used by chloroplasts in the Calvin cycle. In the genome of A. The last one can be subsequently transferred from mitochondria to chloroplasts by a putative bicarbonate carrier in the chloroplast membrane or C4-like pathway; however, the mechanism of such transfer is yet unknown [ ].
The authors suggested that both these CAs play an important role in the growth and development of A. Later, this name started to be used to designate the corresponding stromal CAs in leaves of other plants [ 12 , 15 ].
This enzyme is the second after Rubisco in terms of the amount of protein in the cell 0. The rate of the spontaneous interconversion of Ci forms is low, which implies the role of CA in accelerating the supply of CO 2 to carboxylation centers; however, direct data on the role of the enzyme in this process are lacking.
In some studies, no association of CA activity with photosynthesis was found. Growing plants under conditions of zinc deficiency showed that the rate of photosynthesis in these plants remained almost unchanged with a sharp decrease in CA activity [ ]. However, in these mutants, the carbon isotopic composition of the leaf dry matter was changed. Another group of researchers has found that plants compensated for a decrease in CA activity by increasing the permeability of stomata, which, however, has led to a higher rate of water loss [ ].
In Phaseolus vulgaris plants grown under the increased CO 2 content in the air, a significant decrease in the activities of both CA and Rubisco has been observed [ ]. The activity of these enzymes and the content of transcripts of the genes encoding them were reduced in Pisum sativum plants grown at ppm CO 2 , compared with plants grown at atmospheric carbon dioxide concentration; the transfer of pea plants grown at a carbon dioxide concentration of ppm to the conditions of normal CO 2 content in the atmosphere led to a rapid increase in the expression level of CA and Rubisco genes, following which the activity of the corresponding enzymes in the leaves increased [ 50 ].
One CA in the stroma of chloroplasts was later discovered to be associated with Rubisco on the outside of the thylakoid membrane [ ]. In the early stages of the adaptation of sugar beet plants to a high concentration of carbon dioxide, of ppm, a decrease in both the activity of the soluble and of the membrane-bound CAs was observed.
However, the activity of Rubisco was the same in plants grown in conditions of high CO 2 concentration and in the ambient carbon dioxide content [ ]. The same mechanism of inhibition of CA activity was observed by studying the action of high-temperature stress in the leaves of Helianthus annum [ 11 ]. Nitration, as well as phosphorylation of Tyr, blocks the passage of substrate to active site cavity. It is not entirely clear why the content of CA protein increases with the simultaneous suppression of CA activity.
It can be assumed that plants apply this mechanism to prepare for normal moisture conditions. Water deficit is known to cause stomatal closure with a reduction in plant photosynthetic efficiency and inhibition of Rubisco activity [ ].
These responses often result in a change in photosynthetic and energy metabolism-associated protein accumulation. Herewith Yu et al. Moreover, the same group showed that Arabidopsis thaliana mutant plants over-expressing OsCA1 had a greater salt tolerance. These data imply that the OsCA1 has an important role in the response of plants to environmental stress conditions. This gene, as well as the gene encoding OsCA1, had the chloroplast precursor sequence, which implies the location of both CAs in the chloroplasts in rice.
The latter was detected in the chloroplast stroma in the study of the pathway of newly synthesized proteins into the chloroplast through the endo-membrane system of the Golgi apparatus [ 10 ].
In general, it can be assumed, on the basis of the available data, that plant CAs, as a rule, jointly control one or another metabolic process. Studies using double mutants showed that the reduced synthesis of several CAs had an effect on photosynthesis.
Plants are known to activate anion channels in response to environmental signals such as drought, high levels of carbon dioxide, and bacterial invasion. Abstract As the global atmospheric emissions of carbon dioxide CO 2 and other greenhouse gases continue to grow to record-setting levels, so do the demands for an efficient and inexpensive carbon sequestration system.
Introduction The atmospheric concentrations of greenhouse gases such as carbon dioxide CO 2 , methane, chlorofluorocarbons, and nitrous oxides have been increasing accordingly due to human-induced activities [ 1 ]. Carbonic Anhydrase The need for development of an efficient and inexpensive carbon sequestration system and the drive for an alternative fuel supply have both been led by a group of enzymes called the carbonic anhydrases CAs; EC 4.
Table 1. Figure 1. Schematic of the centralized role for CA in converting CO 2 into beneficial products. The catalytic conversion of CO 2 produced during the combustion of fossil fuels into bicarbonate via CA yields a valuable source of inorganic carbon for algal cultures grown in raceway ponds.
The algal CA can also serve as a great source for calcite CaCO 3 production, being critical in many construction, agricultural, and industrial materials. References J. Hansen, M. Sato, R. Ruedy, A. Lacis, and V. View at: Google Scholar D. View at: Google Scholar R. Spahni, J. Chappellaz, T. Stocker et al. Siegenthaler, T. Stocker, E. Monnin et al. Petit, J.
Jouzel, D. Raynaud et al. Bereiter et al. Pearson and M. View at: Google Scholar K. View at: Google Scholar C. View at: Google Scholar L. View at: Google Scholar J. Houghton, Y. Ding, D. Griggs et al. Aggarwal, C.
Boone, B. Kondeti, and R. View at: Google Scholar V. Krishnamurthy, G. Kaufman, A. Urbach et al. Hewett-Emmett and R. Elleby, L. Chirica, C. Tu, M. Zeppezauer, and S. Huang, Y. Xue, E. Sauer-Eriksson, L. Chirica, S. Lindskog, and B. Liu, P. Bartlow, R. Dilmore et al. Maresca, D. Vullo, A. Scozzafava, and C. View at: Google Scholar I. Nishimori, T. Minakuchi, T. Kohsaki et al. Rowlett, C. McKay et al. Tolvanen, M. The alpha carbonic anhydrase enzymes have been well studied, leading to an understanding of how they work.
Three structures are shown here, showing three steps in the process. The structure at the top PDB entry 5dsj is the empty enzyme. The active site includes a zinc ion magenta , which is held by three histidines purple.
The zinc also coordinates a hydroxide ion red. At bottom left PDB entry 5dsi , carbon dioxide red and gray is bound and a glutamate and a threonine green assist with the reaction.
At bottom right PDB entry 1cam , the hydroxide has been added, forming carbonic acid. The threonine has been mutated to alanine to help capture the complex.
The histidine at upper left green , which was seen in two different conformations in the structure, assists with guiding one of the nearby water molecules orange to the zinc ion, and converting it to a hydroxyl. To explore these three structures in more detail, click on the image for an interactive JSmol.
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Toggle navigation PDB Educational portal of. Molecule of the Month. Carbonic Anhydrase Carbonic anhydrase solubilizes carbon dioxide gas so we can breathe it out Alpha top , beta middle , and gamma bottom carbonic anhydrases. From there, the CO2 is all ready to be exhaled from the lungs and is released through the mouth.
In conclusion, the enzyme carbonic anhydrase is used to balance the blood pH levels, and also to allow humans to breathe out carbon dioxide, more commonly known as CO2. It catalyzes the reaction to convert CO2 to carbonic acid, which breaks down into bicarbonate ions and protons. Coli Recombinant. Shipped with Ice Packs Add to Cart.
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