title: Direct analysis of donor-acceptor distance and relationship to isotope effects and the force constant for barrier compression in enzymatic H-tunneling reactions.
abstract: The role of dynamical effects in enzyme catalysis is both complex and widely debated. Understanding how dynamics can influence the barrier to an enzyme catalyzed reaction requires the development of new methodologies and tools. In particular compressive dynamics-the focus of this study-may decrease both the height and width of a reaction barrier. By making targeted mutations in the active site of morphinone reductase we are able to alter the equilibrium of conformational states for the reactive complex in turn altering the donor-acceptor (D-A) distance for H-transfer. The sub-A changes which we induce are monitored using novel spectroscopic and kinetic "rulers". This new way of detecting variation in D-A distance allows us to analyze trends between D-A distance and the force constant of a compressive dynamical mode. We find that as the D-A distance decreases, the force constant for a compressive mode increases. Further, we demonstrate that-contrary to current dogma-compression may not always cause the magnitude of the primary kinetic isotope effect to decrease.
authors.affiliation: Manchester Interdisciplinary Biocentre, University of Manchester, 131 Princess Street, Manchester, M1 7DN, United Kingdom.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Pudney
authors.forename: Linus O
authors.initials: LO
authors.lastname: Johannissen
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sutcliffe
authors.forename: Sam
authors.initials: S
authors.lastname: Hay
authors.forename: Nigel S
authors.initials: NS
authors.lastname: Scrutton
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006859:Hydrogen; D007554:Isotopes; D056004:Molecular Dynamics Simulation; D016296:Mutagenesis; D009154:Mutation; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D007554:Isotopes; D006859:Hydrogen; D010088:Oxidoreductases; C087820:morphinone reductase