Retention of the oxygens at C-2 and C-3 of D-ribulose 1,5-bisphosphate in the reaction catalyzed by ribulose-1,5-bisphosphate carboxylase.

Ribulose-1,5-bisphosphate carboxylase catalyzes the conversion of D ribulose 1,5-bisphosphate and CO2 to 3-phospho-D-glycerate, with retention of the oxygen atoms at both C-2 and C-3 of the substrate. This observation is consistent with mechanistic pathways involving an enediol intermediate and eliminates suggested mechanisms that involve covalent intermediates between the enzyme and ribulose 1,5-bisphosphate in which the substrate oxygen at C-2 or C-3 is compulsorily lost.