Ribulose-1,5-bisphosphate

Ribulose-1,5-bisphosphate
Identifiers
ChemSpider 110238 Y
ChEBI CHEBI:16710 Y
Jmol-3D images Image 1
Properties
Molecular formula C5H12O11P2
Molar mass 310.09 g mol−1
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Ribulose-1,5-bisphosphate (RuBP) is an organic substance that is involved in photosynthesis. The anion is a double phosphate ester of the ketose (ketone-containing sugar) called ribulose. Salts of this species can be isolated, but its crucial biological function involves this colourless anion in solution. [1] To simplify the presentation, the image in the above table depicts the acid form of this anion.

Role in photosynthesis

The enzyme ribulose bisphosphate carboxylase oxygenase (RuBisCO) catalyzes the reaction between RuBP with carbon dioxide. The product is the highly unstable 6-carbon intermediate known as 3-keto-2-carboxyarabinitol 1,5-bisphosphate. This six-carbon intermediate decays virtually instantaneously into two molecules of glycerate 3-phosphate (G3P) (see figure). Less commonly (e.g. at high temperatures) RuBisCO catalyzes RuBP with oxygen (O2) in a process called photorespiration, a process that occurs at high temperatures in "C3 plants."

In the Calvin Cycle, RuBP is a product of the phosphorylation of ribulose-5-phosphate by ATP.

Used in carbon fixation (of the Calvin cycle):

5-carbon RuBP + 1-carbon CO2 --> 6-carbon intermediate --> 2 3-PGA (3-Phosphoglyceric acid). Each (3-carbon) 3-PGA is then reduced to G3P in carbon reduction. 5 G3P = 3 RuBP. 2 G3P = 1 C6H12O6 (glucose).

References

  1. ^ The topic is discussed in all biochemistry textbooks, this one is representative: Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.