Empirical valence bond calculations of enzyme catalysis

A method that allows one to correlate available x-ray data with activation free energies of enzymic reactions was presented. The method is an Empirical Valence Bond (EVB) approach that uses experimental information to evaluate the energies of the valence bond resonance forms and then calculates the environment-dependent stabilizations of the ionic resonance forms in the enzyme and in solution in order to correlate them with the rate enhancement by the enzyme. The reliability of the method is based on calibration of potential surfaces using solution experiments and on transfer of the calibrated surface to the enzyme active site using only simple electrostatic calculations. The close relation between the method and the intuitive description of bonding provides a new insight into enzymic reactions, describing them as surface crossings between covalent and ionic resonance forms. Such a description clarifies how the stabilization of the ionic resonance forms by the enzyme determines its catalytic activity.