Computer simulation of the triosephosphate isomerase catalyzed reaction.

A major challenge for theoretical simulation methods is the calculation of enzymic reaction rates directly from the three-dimensional protein structure together with some idea of the chemical reaction mechanism. Here, we report the evaluation of a complete free energy profile for all the elementary steps of the triosephosphate isomerase catalyzed reaction using such an approach. The results are compatible with available experimental data and also suggest which of the possible reaction intermediates is kinetically observable. In addition to previously identified catalytic residues, the simulations show that a crystallographically observed active site water molecule plays an important role during catalysis and an intersubunit interaction that could explain the low activity of the monomeric enzyme is also observed. The calculations clearly demonstrate the important catalytic effects associated with stabilization of charged high energy intermediates and reduction of reorganization energy, which are likely to be general principles of enzyme catalyzed charge transfer and separation reactions.