New insights into enzyme catalysis. Ground state tunnelling driven by protein dynamics.

The wave-particle duality of matter suggests that quantum tunnelling may have a prominent role in enzymatic H-transfer. However, unlike for electron tunnelling, evidence for H-tunnelling in enzyme molecules is extremely limited. The theoretical development, and verification by experiment, of a role for protein dynamics in driving enzymatic H-tunnelling is presented. Dynamic theories of H-tunnelling suggest that the kinetic isotope effect, during rupture of a C-H/C-D bond, for example, can assume values interpreted previously as indicating classical transfer. Vibrationally enhanced ground state tunnelling has been demonstrated for enzymes that cleave stable C-H bonds. This is an attractive mechanism as large activation energies make it energetically unfavourable for a classical, over-the-barrier mode of cleavage. Furthermore, it may be a general strategy used by enzymes for catalysing these 'difficult' transformations.