Chemical mechanism of Rubisco catalysis

It is now more than 60 years since D-ribulose-1,5-bisphosphate carboxylase/ oxygenase (EC, Rubisco) was first purified and 50 years since pioneering experiments dealing with its chemical mechanism were reported. Considerable progress has been made to understand the structure of the active site and the complete reaction mechanism, including the roles of several chemical residues of the active site. Rubisco catalyses the carboxylation (CO2 addition) or oxygenation (O2 addition) of D-ribulose-1,5-bisphosphate (RuBP) and the subsequent carbon-carbon cleavage to form two molecules of 3-phospho-D-glycerate (PGA) (with CO2) or one molecule of PGA and one molecule of 2-phospho-glycolate (with O2). Nevertheless, the associated chemical mechanism of the reaction is still incompletely understood and uncertainty remains as to: (i) the chemical form of CO2 or O2 fixed by the enzyme (desolvated or not, activated or not); (ii) intermediate steps and energetics in CO2 and O2 addition; (iii) the specific origin of protons used along the catalytic cycle for reprotonation; and (iv) the specific roles of several residues of the active site.