Rubisco - reaction mechanism
The enzyme ribulose-1,5-bisphosphate carboxylase (rubisco) catalyzes the addition of gaseous carbon dioxide to ribulose-1,5-bisphosphate (RuBP). Product of the reaction are two molecules of 3-phosphoglyceric acid.
C5O3H8(PO42-)2 + CO2 -> 2 C3O3H4PO42-
For the reaction to occur it is neccessary that the protein is activated by the covalent binding of a molecule of carbon dioxide. This CO2 forms a carbamate with the terminal amino group of lysine201. The carbamate itself is labile, it is stabilized in the enzyme by a magnesium ion.
The figures to follow may be viewed in an interactive manner: using the mouse the molecules can be moved; clicking the boxes highlights the described features. Only the first figure is backed by experimental data. Hydrogen atoms (which are not visible in a X-ray data set) were added by a molecular modelling program. The reaction steps were also modeled - there is no claim as to the absolute positions of the atoms concerned. The figures are merely meant to visualize the reaction mechanism.