Transition-state structures for describing the enzyme-catalyzed mechanismsof rubisco

The carboxylation and oxygenation processes of a model substrate, 3,4-dihyd roxy-2-pentanone, have been theoreticaly characterized as a set of steps? m imicking the corresponding reactions of D-ribulose-1,5-bisphosphate catalyz ed by rubisco. A theoretical characterization is carried out of transition- state structures and possible molecular intermediates represented as saddle points of index I and minimum energy structures, respectively. The quantum chemical characterization, at the HF/3-21G calculation level, of these sta tionary points is used to rationalize and to discuss both catalyzed sequenc es. The reported set of these stationary points maps out most experimental aspects of the reaction pathways for the real system.