Abstract
Ribulose-1,5-bisphosphate carboxylase [EC 4.1.1.39, from Rhodospirillum rubrum] catalyzes the conversion of D-ribulose 1,5-bisphosphate and CO2 to 3-phospho-D-glycerate, with retention of the O2 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 O2 at C-2 or C-3 is compulsorily lost.