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Oxygen-dependent H2O2 production by Rubisco.
Following import into chloroplasts and removal of the transit peptide, mature S subunits are assembled with chloroplast-synthesized L subunits to give the active L8S8 Rubisco holoenzyme (21, 22). This assembly process requires the assistance of another chloroplast protein (23) now known as chaperonin 60 (cpn60) (24, 25). In fact, studies on the assembly of Rubisco in chloroplasts and bacteria (23, 26, 27) led to the discovery of the molecular chaperone cpn60 and its role in the correct folding of Rubisco and many other proteins (24, 25, 28). Productive folding of Rubisco requires Mg , ATP hydrolysis, and a smaller cochaperonin molecule (29). Cpn60-mediated folding of Rubisco in bacteria uses a cochaperonin oligomer with 10-kDa subunits (24), but the folding of Rubisco in chloroplasts seems to involve a co-chaperonin oligomer with 21-kDa subunits (30). The reason for this larger cochaperonin in chloroplasts and the mechanistic details of the Rubisco assembly process in plants are currently under investigation.
Figure 2. The organization of the subunits of L8 S8 Rubisco. In (A) the display is from above the fourfold axis of symmetry of the enzyme. The four L-subunit dimers are shown only schematically by a light trace of the positions of the Ca atoms of the backbone, whereas the structural elements of the S subunits have been displayed with Molscript. The four S subunits shown reside at the top of the molecule situation between each L-subunit dimer, with a loop extending into, but not obscuring, the prominent central channel of the L 8 core. In (B), the other four S subunits are found to occupy the same position at the bottom of the core.
The Reactions Catalyzed by Rubisco
The inner chloroplast membrane have a specific antiporter thatcatalyzes the one-for-one exchange of Pi with a triosephosphate, either dihydroxyacetone phosphate or 3-phosphoglycerate (Fig. 18–7).This antiporter simultaneously moves Pi into the chloroplast, where it is usedin photophosphorylation, and moves triose phosphate into the cytosol, where itcan be used to synthesize sucrose, the form in which the fixed carbon istransported to distant plant tissues. Sucrose synthesis in the cytosol andstarch synthesis in the chloroplast are the major pathways by which the excesstriose phosphate from photosynthesis is “harvested.” Sucrose synthesis releasesfour Pi molecules from the four triose phosphates requiredfor its production. For every molecule of triosephosphate removed from the chloroplast, one Pi is transportedinto the chloroplast, providing the ninth Pi mentionedabove, to be used in regenerating ATP. If this exchangewere blocked, triose phosphate synthesis wouldquickly deplete the available Pi in the chloroplast, slowingATP synthesis and suppressing assimilation of CO2into starch.
FIGURE 18–7 The Pi–triose phosphate antiport system of the innerchloroplast membrane. This transporter facilitates the exchange ofcytosolic Pi for stromal dihydroxyacetone phosphate. The products ofphotosynthetic carbon assimilation are thus moved into the cytosolwhere they serve as a starting point for sucrose biosynthesis, and Pirequired for photophosphorylation is moved into the stroma.
Rubisco synthesis, turnover and degradation: Some …
Effects of Rubisco kinetics and Rubisco activation state on the temperature dependence of the photosynthetic rate in spinach leaves from contrasting growth temperatures.
The gene for the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit relocated to the plastid genome of tobacco directs the synthesis of small subunits that assemble into Rubisco.
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Production of the Escherichia coli betaine-aldehyde dehydrogenase, an enzyme required for the synthesis of the osmoprotectant glycine betaine, in transgenic plants.
Changes in the Synthesis of Rubisco in ..
The Chlamydomonas reinhardtii cia3 mutant lacking a thylakoid lumen-localized carbonic anhydrase is limited by CO2 supply to Rubisco and not photosystem II function in vivo.
from protein synthesis to health and disease to biological energy
Regulation of ribulose-1,5-bisphosphate carboxylase/oxygenase by carbamylation and 2-carboxyarabinitol 1-phosphate in tobacco: insights from studies of antisense plants containing reduced amounts of Rubisco activase.
CiNii 論文 - Rubisco: Photosynthesis and its protein …
A dynamic model of photosynthesis in varying light taking account of stomatal conductance, C3-cycle intermediates, photorespiration and Rubisco activation.
RUBISCO | Active Site | Photosynthesis - Scribd
As we have seen, photosynthetic cells produce O2 (by the splitting of H2O)and use CO2 to produce 3-phosphoglycerate with a net gaseous changeduring photosynthesis that can be written as follow:
CO2 + H2O → O2 + (CH2O)
In the dark plants are carrying out mitochondrial respiration bythe oxidation of substrates to CO2 and theconversion of O2 to H2O. On top of that, there is another processin plants that, like mitochondrial respiration, consumesO2 and produces CO2 and, like photosynthesis, is drivenby light. This process is called photorespiration and is a costlyside reaction of photosynthesis. In this section we describethis process and the strategies plants use tominimize its metabolic consequences.
and glycolate metabolism is the bifunctional nature of Rubisco
Certain plants produce high levels of CO2 which helps reducing the energy wasting effect of photorespiration by competing with molecular oxygen for Rubisco.
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