Good vibrations in enzyme-catalysed reactions

Fast motions (femtosecond to picosecond) and their potential involvement during enzyme-catalysed reactions have ignited considerable interest in recent years. Their influence on reaction chemistry has been inferred indirectly from studies of the anomalous temperature dependence of kinetic isotope effects and computational simulations. But can such motion reduce the width and height of energy barriers along the reaction coordinate, and contribute to quantum mechanical and/or classical nuclear-transfer chemistry? Here we discuss contemporary ideas for enzymatic reactions invoking a role for fast 'promoting' (or 'compressive') motions that, in principle, can aid hydrogen-transfer reactions. Of key importance is the direct demonstration of a role for compressive motions and the ability to understand in atomic detail the structural origin of these fast motions, but so far this has not been achieved. Here we discuss both indirect experimental evidence that supports a role for compressive motion and the additional insight gained from computational simulations.