Enzymes are propelled by the acoustic wave created during a chemical reaction

One of the most important physico-chemical discoveries made by mankind is that matter is made of atoms. These atoms can create covalent bonds to form molecules. During a chemical reaction (the re-arrangement of these atoms to create a new molecule) covalent bonds are made or broken and a given amount of energy is released (typically around ~ 100 kcal/mol). This energy has been well characterized in bulk and corresponds to the enthalpy of the chemical reaction. However, very little attention has been paid to the energy released at the single molecule level.

HFSP Cross-Disciplinary Fellow Clement Riedel and colleagues
authored on Fri, 23 January 2015

Enzymes catalyze chemical reactions. They are an essential element of the biological realm because if all reactions occurred without enzymes, the reaction would be so slow that life could not be sustained. It is known that enzymes increase chemical reaction rates by lowering the activation energy of those reactions and, since the pioneering studies of Michaelis and Menten, have been assumed to remain unaltered during the process. The heat released during a chemical reaction is much greater than the energies maintaining the stability of the catalyst itself.


 

Figure: Illustration of enzymes propelled by the acoustic wave created during a chemical reaction. Image Copyright ©2014 iSO-FORM  LLC.

Recently it was found that the diffusion coefficient of enzymes, as measured in Fluorescence Correlation Spectroscopy (FCS) experiments, increases significantly in the presence of their substrate (Muddana, H. S. et al., JACS,132(7), 2110 (2010)). The authors originally formulated an ‘electrophoretic’ model to explain the phenomenon and more recently a ‘chemotactic’ one, upon observing the same effect for reactions that do not result in charged products. Using different enzymes, we have shown that the increase in diffusion coefficient is related the amount of heat released by the reaction during each turnover. A key point of this study is that enzymes with large enthalpy exhibit a high enhanced diffusion while enzymes with nearly null enthalpy do not. According to our model, the reaction produces a heat wave that propagates from the active site of the enzyme, deforming it against the protein-surface interface, giving rise to a recoil effect that effectively propels the enzyme during each catalytic event. We formulate a stochastic theory that predicts the increase in diffusion coefficient to be proportional to the rate of the reaction, as is indeed observed experimentally. This formulation also shows that the coefficient of proportionality depends linearly on the enthalpy of the reaction.

Our results suggest a crucial re-thinking of the current paradigm of enzyme catalysis: with the energy released easily one order of magnitude larger than the free energy stabilizing the protein catalyst. It is not unthinkable that many enzymes may partly unfold after each catalytic event and that their turnover measured in bulk may include a ‘dead time’ while the enzyme regains its active structure. Similarly, we speculate that some enzymes, particularly those that function as molecular motors, may have evolved to ‘channel’ the energy released after each catalytic event to help propel them along their tracks.

We believe that this work should be of interest to a broad range of scientists, including enzymologists, biochemists, biophysicists, and in general, those interested in energy exchange and energy flow phenomena at the nano scale.

Reference

The heat released during catalytic turnover enhances the diffusion of an enzyme. Clement Riedel, Ronen Gabizon, Christian A. M. Wilson, Kambiz Hamadani, Konstantinos Tsekouras, Susan Marqusee, Steve Pressé & Carlos Bustamante. Nature 517, 227–230 (08 January 2015) doi:10.1038/nature14043.

Pubmed link