Statistical Physics of Active Enzyme Suspensions

Understanding the dynamics of biomolecules is crucial if we are to fully appreciate and potentially harness their functionalities in the search for biocompatible micro- and nanomachines. However, there are currently many obstacles obscuring the path to a complete description at the fundamental level that would allow for the design and fabrication of such machines. The intrigue and complication is increased by the variety of biomolecular species, meaning that there are many possible applications, but also that their physical properties do not obviously fit into one universality class. For example, a variety of propulsion mechanisms have been observed and predicted for microscopic swimmers. Enzymes have received a lot attention for their ability to perform very specific functions at nanoscales under conditions dominated by thermal fluctuations and viscous hydrodynamics. Recently, the question of the effect of catalytic activity of enzymes on their diffusion properties has been studied. Experiments with dilute solutions of enzyme molecules which catalyse exothermic reactions and typically have high catalytic rates have revealed that their diffusion is substantially enhanced in a way that is dependent on the substrate concentration when they are catalytically active. Accordingly, there have been theoretical investigations into the underlying mechanism of the phenomenon, such as explanations founded on the exothermicity and fast rate of catalysis of the chemical cycle of the enzyme. The effect of hydrodynamic coupling of enzyme molecules to their environment has also been studied. All of the theories proposed so far relied on the idea that the catalytic cycle is out of equilibrium, or fail to accurately describe the experimental evidence without very specific atypical assumptions. Furthermore, the observation appears to be generic: Recent experiments have demonstrated enhanced diffusion in the endothermic and slow enzyme aldolase. The phenomenon is observed for a wide range of enzymes with very different chemical properties, which were not captured by existing theoretical frameworks for enhanced diffusion. Therefore, we investigate a new theoretical approach to the understanding of this physical phenomenon, capable of replicating all of the experimental evidence. With this, we hope to propose a new universal theory for enhanced diffusion of enzyme molecules which is independent of their non-physical properties.
This project falls within the EPSRC physical sciences grand challenges of Emergence and Physics Far from Equilibrium, Nanoscale Design of Functional Materials, and Understanding the Physics of Life.