%0 Journal Article %A Meyer, Matthew P. %A Klinman, Judith P. %D 2011 %T Investigating Inner-Sphere Reorganization via Secondary Kinetic Isotope Effects in the C−H Cleavage Reaction Catalyzed by Soybean Lipoxygenase: Tunneling in the Substrate Backbone as Well as the Transferred Hydrogen %U https://acs.figshare.com/articles/journal_contribution/Investigating_Inner_Sphere_Reorganization_via_Secondary_Kinetic_Isotope_Effects_in_the_C_H_Cleavage_Reaction_Catalyzed_by_Soybean_Lipoxygenase_Tunneling_in_the_Substrate_Backbone_as_Well_as_the_Transferred_Hydrogen/2696359 %R 10.1021/ja1050742.s001 %2 https://ndownloader.figshare.com/files/4372315 %K deuterium isotope effect %K Substrate Backbone %K cleavage %K force constants %K measurement %K electron transfer %K Transferred HydrogenThis work %K substrate linoleic acid %K tunneling correction %K NMR %K 13 C KIEs %K 13 C isotope effects %K C 11 %K Secondary Kinetic Isotope Effects %K LA %K isotope effects %K nonclassical behavior %K torsional strain %K reactive C 11 position %K Soybean Lipoxygenase %X This work describes the application of NMR to the measurement of secondary deuterium (2° 2H) and carbon-13 (13C) kinetic isotope effects (KIEs) at positions 9−13 within the substrate linoleic acid (LA) of soybean lipoxygenase-1. The KIEs have been measured using LA labeled with either protium (11,11-h2-LA) or deuterium (11,11-d2-LA) at the reactive C11 position, which has been previously shown to yield a primary deuterium isotope effect of ca. 80. The conditions of measurement yield the intrinsic 2° 2H and 13C KIEs on kcat/Km directly for 11,11-d2-LA, whereas the values for the 2° 2H KIEs for 11,11-h2-LA are obtained after correction for a kinetic commitment. The pattern of the resulting 2° 2H and 13C isotope effects reveals values that lie far above those predicted from changes in local force constants. Additionally, many of the experimental values cannot be modeled by electronic effects, torsional strain, or the simple inclusion of a tunneling correction to the rate. Although previous studies have shown the importance of extensive tunneling for cleavage of the primary hydrogen at C11 of LA, the present findings can only be interpreted by extending the conclusion of nonclassical behavior to the secondary hydrogens and carbons that flank the position undergoing C−H bond cleavage. A quantum mechanical method introduced by Buhks et al. [J. Phys. Chem. 1981, 85, 3763] to model the inner-sphere reorganization that accompanies electron transfer has been shown to be able to reproduce the scale of the 2° 2H KIEs. %I ACS Publications