Residues with considerable interactions (E=|5 kcal/mol|) are shown in table 1. As is seen from the table, most residues that have significant contribution are evolutionarily conserved, in particular residues closer to the active site. Of the residues with favorable interactions in the reactant, residue Q894 has considerably higher favorable interaction in the reactant in both the systems (23.6 kcal/mol for Mg 2+ system and 12.7 kcal/mol for Mn 2+ system). Among the residues with favorable interactions with the active site, stronger interactions are exhibited by G923 (13.8 kcal/mol) and R1190 (21.1 kcal/mol) in the system with Mg 2+ ions, whereas residue A676(-15.0 kcal/mol) shows a strong favorable interaction in the system with Mn 2+ ions. It is interesting to note that G923 shows more favorable interactions towards the active site of the transition state in presence of Mg 2+ ions, whereas for Mn 2+ ions it shows more favorable interactions in the reactant.