Download MendeleyExtremely elevated room-temperature kinetic isotope effects quantify the critical role of barrier width in enzymatic C-H activation.
Hu, S., Sharma, S.C., Scouras, A.D., Soudackov, A.V., Carr, C.A., Hammes-Schiffer, S., Alber, T., Klinman, J.P.(2014) J Am Chem Soc 136: 8157-8160
- PubMed: 24884374
- DOI: https://doi.org/10.1021/ja502726s
- Primary Citation of Related Structures:
4WHA - PubMed Abstract:
The enzyme soybean lipoxygenase (SLO) has served as a prototype for hydrogen-tunneling reactions, as a result of its unusual kinetic isotope effects (KIEs) and their temperature dependencies. Using a synergy of kinetic, structural, and theoretical studies, we show how the interplay between donor-acceptor distance and active-site flexibility leads to catalytic behavior previously predicted by quantum tunneling theory. Modification of the size of two hydrophobic residues by site-specific mutagenesis in SLO reduces the reaction rate 10(4)-fold and is accompanied by an enormous and unprecedented room-temperature KIE. Fitting of the kinetic data to a non-adiabatic model implicates an expansion of the active site that cannot be compensated by donor-acceptor distance sampling. A 1.7 Å resolution X-ray structure of the double mutant further indicates an unaltered backbone conformation, almost identical side-chain conformations, and a significantly enlarged active-site cavity. These findings show the compelling property of room-temperature hydrogen tunneling within a biological context and demonstrate the very high sensitivity of such tunneling to barrier width.
Organizational Affiliation:
Department of Chemistry, University of California , Berkeley, California 94720, United States.
