4wha

Publication Abstract from PubMed

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 A 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.

Extremely elevated room-temperature kinetic isotope effects quantify the critical role of barrier width in enzymatic C-H activation.,Hu S, Sharma SC, Scouras AD, Soudackov AV, Carr CA, Hammes-Schiffer S, Alber T, Klinman JP J Am Chem Soc. 2014 Jun 11;136(23):8157-60. doi: 10.1021/ja502726s. Epub 2014 Jun, 2. PMID:24884374^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.