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Calvin cycle

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The Calvin cycle has thirteen reactions catalyzed by eleven enzymes. It shares five enzymes with gluconeogenesis and three with the pentose phosphate pathway. The remaining three enzymes are largely exclusive to the Calvin cycle. The characteristic enzyme of the Calvin cycle, rubisco, catalyzes the carboxylation of ribulose 1,5-bisphosphate (RuBP). Rubisco also catalyzes a fourteenth reaction, the oxygenation of RuBP, initiating photorespiration which bleeds carbon and energy from the cycle and reduces its efficiency. The Calvin cycle maintains a hexose phosphate pool, a pentose phosphate pool, and a triose phosphate pool.

The Calvin cycle is autocatalytic because it can bootstrap itself from just triose phosphate, carbon dioxide, NADPH, and ATP. Autocatalysis typical of autotrophic carbon fixation pathways. The Calvin cycle can be divided, for convenience, into three phases.

Carboxylation phase

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1, 1a. rubisco (EC 4.1.1.39)

RuBP + CO2 + H2O --> 2(3-PGA)
RuBP + O2 --> 3-PGA + 2-phosphoglycolate

Reduction phase

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The reduction phase reduces 3-PGA to GAP, contributes GAP and DHAP to the triose phosphate pool, and contributes fructose 6-phosphate to the hexose phosphate pool. The reduction phase is just gluconeogenesis.

2. phosphoglycerate kinase (EC 2.7.2.3)

3-PGA + ATP <-> 1,3-bisphosphoglycerate + ADP

3. glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) and (EC 1.2.1.59)

1,3-bisphosphoglycerate + NADPH + H(+) <-> GAP + NADP(+) + Pi

3a. glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12)

1,3-bisphosphoglycerate + NADH + H(+) <-> GAP + NAD(+) + Pi

4. triose-phosphate isomerase (EC 5.3.1.1)

GAP <-> DHAP

5. fructose-bisphosphate aldolase (EC 4.1.2.13)

DHAP + GAP <-> fructose 1,6-bisphosphate

6. fructose 1,6-bisphosphatase (EC 3.1.3.11)

fructose 1,6-bisphosphate + H2O --> fructose 6-phosphate + Pi

Regeneration phase

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The regeneration phase uses fructose 6-phosphate and triose phosphate to regenerate RuBP, and contributes xylulose 5-phosphate, ribose 5-phosphate, and ribulose 5-phosphate to the pentose phosphate pool.

7. transketolase (EC 2.2.1.1)

GAP + fructose 6-phosphate <-> xylulose 5-phosphate + erythrose 4-phosphate

8. fructose-bisphosphate aldolase (EC 4.1.2.13)

DHAP + erythrose 4-phosphate <-> sedoheptulose 1,7-bisphosphate

9. sedoheptulose-bisphosphatase (EC 3.1.3.37)

sedoheptulose 1,7-bisphosphate + H2O --> sedoheptulose 7-phosphate + Pi

10. transketolase (EC 2.2.1.1)

GAP + sedoheptulose 7-phosphate <-> xylulose 5-phosphate + ribose 5-phosphate

11. ribulose-phosphate 3-epimerase (EC 5.1.3.1)

xylulose 5-phosphate <-> ribulose 5-phosphate

12. ribose-5-phosphate isomerase (EC 5.3.1.6)

ribose 5-phosphate <-> ribulose 5-phosphate

13. phosphoribulokinase (EC 2.7.1.19)

ribulose 5-phosphate + ATP --> RuBP + ADP

Intermediates

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  1. RuBP
  2. 3-PGA
  3. 2-phosphoglycolate
  4. 1,3-bisphosphoglycerate
  5. GAP
  6. DHAP
  7. fructose 1,6-bisphosphate
  8. fructose 6-phosphate
  9. xylulose 5-phosphate
  10. erythrose 4-phosphate
  11. sedoheptulose 1,7-bisphosphate
  12. sedoheptulose 7-phosphate
  13. ribose 5-phosphate
  14. ribulose 5-phosphate

Sugars

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Calvin cycle sugars in linear form

  1. D-glyceraldehyde: (2R)-2,3-dihydroxypropanal
  2. dihydroxyacetone: 1,3-dihydroxypropan-2-one
  3. D-erythrose: (2R,3R)-2,3,4-trihydroxybutanal
  4. D-ribose: (2R,3R,4R)-2,3,4,5-tetrahydroxypentanal
  5. D-ribulose: (3R,4R)-1,3,4,5-tetrahydroxypentan-2-one
  6. D-xylulose: (3S,4R)-1,3,4,5-tetrahydroxypentan-2-one
  7. D-fructose: (3S,4R,5R)-1,3,4,5,6-pentahydroxyhexan-2-one
  8. D-sedoheptulose: (3S,4R,5R,6R)-1,3,4,5,6,7-hexahydroxyheptan-2-one

Cyclic forms of fructose

  • alpha-D-fructofuranose: (2S,3S,4S,5R)-2,5-bis(hydroxymethyl)oxolane-2,3,4-triol
  • beta-D-fructofuranose: (2R,3S,4S,5R)-2,5-bis(hydroxymethyl)oxolane-2,3,4-triol
  • alpha-D-fructopyranose: (2S,3S,4R,5R)-2-(hydroxymethyl)oxane-2,3,4,5-tetrol
  • beta-D-fructopyranose: (2R,3S,4R,5R)-2-(hydroxymethyl)oxane-2,3,4,5-tetrol

Glucose

  • D-glucose: (2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanal
  • alpha-D-glucopyranose: (2S,3R,4S,5S,6R)-6-(hydroxymethyl)oxane-2,3,4,5-tetrol
  • beta-D-glucopyranose: (2R,3R,4S,5S,6R)-6-(hydroxymethyl)oxane-2,3,4,5-tetrol

GAPDH articles

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Willow

New redirect

Not Willow

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Fructose-bisphosphate aldolase

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See article.

Aldolase (disambiguation)

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See article.

Glyceraldehyde-3-phosphate dehydrogenase (NADP+)

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See article.

Glyceraldehyde-3-phosphate dehydrogenase (disambiguation)

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See article.

Glyceraldehyde-3-phosphate dehydrogenase (NADP+) (phosphorylating)

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See article.
glyceraldehyde-3-phosphate dehydrogenase (NADP+) (phosphorylating)
Identifiers
EC no.1.2.1.13
CAS no.37250-87-6
Databases
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BRENDABRENDA entry
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MetaCycmetabolic pathway
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Reactions

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Glyceraldehyde-3-phosphate dehydrogenase (NADP+) (phosphorylating) catalyzes

GAP + NADP+ + Pi ⇌ 1,3-bisphosphoglycerate + NADPH + H+

In the Calvin cycle

RuBP + CO2 + H2O → 2(3-PG)
3-PG + ATP ⇌ 1,3-bisphosphoglycerate + ADP
1,3-bisphosphoglycerate + NADPH + H+ ⇌ GAP + NADP+ + Pi

Triose-phosphate isomerase maintains DHAP and GAP in near equilibrium, producing the mixture called triose phosphate (TP)

GAP ⇌ DHAP

Scratch

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