Catalytic mechanism of enzymes: preorganization, short strong hydrogen bond, and charge buffering.

During the past decade, there has been much debate about the enormous catalytic rate enhancement observed in enzymatic reactions involving carbanion intermediates. Our recent theoretical study has demonstrated the importance of the short strong hydrogen bond (SSHB) in the enzymatic reactions. Nevertheless, other recent theoretical studies espouse the role of preorganization over that of the SSHB. To achieve a consensus on this issue and to find the truth, a more clarified explanation must be given. To this end, we have carried out an elaborate analysis of these enzymatic reactions. We here clarify that the catalytic mechanism needs to be explained with three important factors, viz., SSHB, preorganization, and charge buffering/dissipation. Since the charge buffering role is different from the commonly used concepts of the SSHB and preorganization (unless these definitions are expanded), we stress that the charge buffering role of the catalytic residues is an important ingredient of the enzymatic reaction in reducing the level of accumulation of the negative charge on the substrate during the reaction process. This charge reduction is critical to the lowering of activation barriers and the stabilization of intermediates.