Ribulose 1,5-bisphosphate
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/93/RuBP-2D-skeletal.png/300px-RuBP-2D-skeletal.png)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/4/40/RuBP-3D-balls.png/300px-RuBP-3D-balls.png)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/RuBP.jpg/300px-RuBP.jpg)
Ribulose-1,5-bisphosphate (RuBP) is the molecule that carbon dioxide reacts with in photosynthetic carbon fixation. The enzyme ribulose bisphosphate carboxylase oxygenase(RuBisCO) catalyzes RuBP with carbon dioxide in order to synthesize a highly unstable 6-carbon intermediate known as 3-keto-2-carboxyarabinitol 1,5-bisphosphate, which decays virtually instantaneously into two molecules of glycerate 3-phosphate (G3P) (see Calvin Cycle).
RuBP is both used and created during the Calvin Cycle. It 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 3PG. Each (3-carbon) 3PG is then reduced to G3P in carbon reduction. 5 G3P = 3 RuBP. 2 G3P = 1 C6H12O6 (glucose).