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MetNet - plant pathway - Calvin-Benson-Bassham cycle
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Pathway details: Calvin-Benson-Bassham cycle


General info Interaction details Linked pathways Protein-protein interactions
Notes
  Pathway was created on Mon Jul 29, 2013.
 Contributed by junyoni:
General Information: Rubisco (ribulose bisphosphate carboxylase/oxygenase) is a bifunctional enzyme that catalyzes both the carboxylation and oxygenation of D-ribulose-1,5-bisphosphate (RuBP). The carboxylation process is generally known as CO2 fixation (this pathway) whereas the oxygenation process is known as photorespiration (photorespiration). This pathway is the only pathway in plants that can catalyze the net fixation of CO2. Indeed, globally through the action of the metabolic process, three molecules CO2 are combined along with one Pi into a three-carbon sugar phosphate (D-glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, which interconvert and are also known as triose-P) |CITS:[BOWYER97]|. This cycle occurs in the stroma of the chloroplasts. It is composed of 13 reactions catalyzed by 11 enzymes. The pathway has three distinct phases: (i) one of the major steps of the pathway is the carboxylation of RuBP by Rubisco into two molecules of 3-phosphoglycerate; (ii) the reduction of 3-phosphoglycerate into triose-P; and (iii) the regeneration of the primary acceptor RuBP. As a result, it takes three turns of the cycle to generate one net molecule of triose-P. This triose-P can have several fates: it can be used (i) to generate more RuBP (five turns of the cycle will generate an additional RuBP molecule if triose-P is reinvested); (ii) to produce starch in the chloroplast (see starch biosynthesis); (iii) to produce sucrose (see gluconeogenesis); or (iv) to be converted into 3-phosphoglycerate, thereby generating ATP and reductant [NAD(P)H] (Note: the latter two conversions occur in the cytosol and require triose-P to be exported from the chloroplast via the phosphate translocator in exchange from Pi from the cytosol). The Calvin cycle has many regulatory points of control, some of which are reviewed in |CITS:[Bowyer97]|. Three factors will be noted here that determine the rate of cycling of the pathway: (i) the rate of utilization of triose-P for the synthesis of carbohydrates and other compounds, (ii) light by way of the electron transport at the level of the redox regulation by the thioredoxin system, the modulation of enzymatic activity by NADPH and ATP, and changes in stromal pH and Mg2+; and (iii) the regulation of Rubisco by CO2 (of which the regulation by 2-carboxy-D-arabinitol 1-phosphate is an element; see CA1P biosynthesis).
  Parts of this pathway occur in:   plastid stroma     cytosol     plastid     nucleus     mitochondrion  


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metabolite [31]
RNA [57]
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gene [57]
protein complex [27]


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