Simple model for the effect of Glu165----Asp165 mutation on the rate of catalysis in triose phosphate isomerase.

We present an ab-initio self-consistent field calculation with a 4-31G basis set on a simple model for proton abstraction from hydroxyacetone (a model for dihydroxyacetone phosphate; DHAP) by formate, which is a model for Glu165 in triose phosphate isomerase. Earlier, we showed that the electrophilic groups on the enzyme (the NH3+ of Lys13 and the NH of His95) were essential to efficient catalysis by triose phosphate isomerase. These groups stabilized the enediolate formed by proton abstraction from the DHAP model so that proton transfer from this molecule to Glu165 became likely. In this study, we carry this analysis one step further. First, we re-examine the energy profile for proton transfer, using the fact that our earlier calculations showed that the combined effect of His95 and Lys13 on the reactant DHAP and intermediate enediolate was to make them equal in energy. Then, we analyze the likely effect of changing Glu165 to Asp165 and relate this to experiments on the kinetics of enzyme catalysis by the Glu165----Asp165 mutant.