Ribulose 1,5-bisphosphate

structural formula for ribulose-1,5-biphosphate

ball and stick model for ribulose-1,5-biphosphate

spacefilling model for ribulose-1,5-biphosphate

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).