| Abstrakt: |
The theory of absolute reaction rates implies that the grip of a catalyst on a substrate tightens with substrate activation, relaxing later as products are formed and released. Analogs that mimic different kinds of substrate activation can, through the structural details of their complexes with enzymes, indicate how active site residues are involved in the enhancement of reactions rates. In several cases, bonds involved in general acid-base catalysis have been identified tentatively; and recent evidence points to a hydrogen bond of remarkable stability in the transition state in enzymatic deamination of adenosine. Similar approaches have been used to enzymes that act primarily by substrate distortion, nucleophilic catalysis, solvent removal and catalysis by approximation. Two recurring observations, that were not expected in theory, have been the binding of inhibitors in ionized forms that are rare in solution, and changes in enzyme configuration that accompany binding of transition state analogs. Origins and implications of these findings will be discussed with specific reference to the role of solvent water in catalytic phenomena. |
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