ribuloosi15bisfosfaadiga

Ribuloosi-1,5-bisfosfaat (RuBP) is an organic compound with the formula C5H12O11P2. It is a crucial molecule in the Calvin cycle, the light-independent reactions of photosynthesis. RuBP is a five-carbon sugar molecule that is phosphorylated at the 1 and 5 positions. In the Calvin cycle, atmospheric carbon dioxide is fixed by attaching it to RuBP, a reaction catalyzed by the enzyme RuBisCO (ribulose-1,5-bisfosfaat karboksülaas/oksügenaas). This initial step produces an unstable six-carbon intermediate that immediately breaks down into two molecules of 3-fosfoglütseraat. Subsequent steps in the Calvin cycle then regenerate RuBP, allowing the cycle to continue. The regeneration of RuBP requires energy in the form of ATP and reducing power in the form of NADPH, both of which are produced during the light-dependent reactions of photosynthesis. Therefore, RuBP plays a central role in converting light energy into chemical energy stored in organic molecules. Its availability and the efficiency of its regeneration are key factors determining the rate of carbon fixation in plants and other photosynthetic organisms.