The observation that hydrogen transfer occurs by quantum mechanical tunneling across all classes of C-H activation (H+, H:- and H. transfer ) has fundamental consequences for our views of enzyme catalysis. A key feature is the inherent temperature independence of the movement of hydrogen as a wave, implicating the “environment’ as the source of the enthalpic barrier to catalysis. Modified versions of Marcus theory have emerged to explain ktun, and these can be applied to the enzymatic kcat by incorporating a term that accounts for the fact that catalysis is also determined by the (small) fraction of enzymatic sub-states that achieve tunneling ready states: kcat=Fconf ktun. This talk will focus on the protein environmental reorganization term within ktun as the major parameter controlling ΔH‡. Experimental methods have been developed to first obtain spatial resolution of thermal conduit(s) that lead from solvent to the enzyme active site and second to study the role of these conduits via kinetic measurements such as temperature dependent (ns-ps) Stokes shifts and (μs) FRET. The talk will conclude with emerging examples of thermal conduits within many different classes of enzyme reactions, extending the picture of catalytic origins from C-H activation to enzymes in general.
Judith Klinman / University of California, Berkeley
Event Details & Abstracts