Ribulose-1,5 -biphosphate carboxylase oxygenase

A ribulose-1,5 -biphosphate carboxylase/oxygenase Mg2+ formation of an enediol(ate) addition of either C02 or 02/C-C bond cleavage... 

Martin, J. S. and M. M. Martin, Taimin assays in ecological studies. Precipitation of ribulose-1,5-biphosphate carboxylase/ oxygenase by tannic acid, quebracho, and oak foliage extracts, J. Chem. Ecol., 9, 285-294 (1983). 

H2CO is an abbreviation for a carbohydrate. The reaction is a part of the Calvin cycle. The enzyme necessary to carry out the binding of CO2 is called ribulose-1,5-biphosphate carboxylase oxygenase (RuBisCO). The mechanisms are not fully known. The cofactor ribulose-1,5-biphosphate, a rather small sugar phosphate molecule, binds to CO2 after abstraction of a proton. A covalent bond is formed between RuBis and CO2 (Figure 15.12). 

Atmospheric CO2 first moves through the stomata, dissolves into leaf water and enters the outer layer of photosynthetic cells, the mesophyll cell. Mesophyll CO2 is directly converted by the enzyme ribulose biphosphate carboxylase/oxygenase ( Rubisco ) to a six carbon molecule that is then cleaved into two molecules of phosphoglycerate (PGA), each with three carbon atoms (plants using this photosynthetic pathway are therefore called C3 plants). Most PGA is recycled to make ribulose biphosphate, but some is used to make carbohydrates. Free exchange between external and mesophyll CO2 makes the carbon fixation process less efficient, which causes the observed large C-depletions of C3 plants. 

Jordan DB, Ogren WL Species variation in the specificity of ribulose biphosphate carboxylase/oxygenase, Afafure 291 513—515, 1981. 

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