title: Quantum chemical modeling of the kinetic isotope effect of the carboxylation step in RuBisCO.
abstract: Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most important enzyme for the assimilation of carbon into biomass, features a well-known isotope effect with regards to the CO(2) carbon atom. This kinetic isotope effect α = k(12)/k(13) for the carboxylation step of the RuBisCO reaction sequence, and its microscopic origin, was investigated with the help of cluster models and quantum chemical methods [B3LYP/6-31G(d,p)]. We use a recently proposed model for the RuBisCO active site, in which a water molecule remains close to the reaction center during carboxylation of ribulose-1,5-bisphosphate [B. Kannappan, J.E. Gready, J. Am. Chem. Soc. 130 (2008), 15063]. Alternative active-site models and/or computational approaches were also tested. An isotope effect alpha for carboxylation is found, which is reasonably close to the one measured for the overall reaction, and which originates from a simple frequency shift of the bending vibration of (12)CO(2) compared to (13)CO(2). The latter is the dominant mode for the product formation at the transition state.
authors.affiliation: Theoretische Chemie, Institut für Chemie, Universität Potsdam, Potsdam-Golm, Germany. goetze@mpi-muelheim.mpg.de
authors.forename: Jan Philipp
authors.initials: JP
authors.lastname: Götze
authors.forename: Peter
authors.initials: P
authors.lastname: Saalfrank
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D002247:Carbon Isotopes; D020134:Catalytic Domain; D007700:Kinetics; D008954:Models, Biological; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology; D011789:Quantum Theory; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry* / Q000378:metabolism; D012274:Ribulosephosphates / Q000737:chemistry* / Q000378:metabolism; D018724:Spinacia oleracea / Q000201:enzymology; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D012274:Ribulosephosphates; D014867:Water; D002245:Carbon Dioxide; C001933:ribulose-1,5 diphosphate; D012273:Ribulose-Bisphosphate Carboxylase