title: 13C isotope effect on the reaction catalyzed by prephenate dehydratase.
abstract: The (13)C isotope effect for the conversion of prephenate to phenylpyruvate by the enzyme prephenate dehydratase from Methanocaldococcus jannaschii is 1.0334+/-0.0006. The size of this isotope effect suggests that the reaction is concerted. From the X-ray structure of a related enzyme, it appears that the only residue capable of acting as the general acid needed for removal of the hydroxyl group is threonine-172, which is contained in a conserved TRF motif. The more favorable entropy of activation for the enzyme-catalyzed process (25 eu larger than for the acid-catalyzed reaction) has been explained by a preorganized microenvironment that obviates the need for extensive solvent reorganization. This is consistent with forced planarity of the ring and side chain, which would place the leaving carboxyl and hydroxyl out of plane. Such distortion of the substrate may be a major contributor to catalysis.
authors: Institute for Enzyme Research and Department of Biochemistry, University of Wisconsin, Madison, WI, USA.
authors: Jeremy
authors: J
authors: Van Vleet
authors: Andreas
authors: A
authors: Kleeb
authors: Peter
authors: P
authors: Kast
authors: Donald
authors: D
authors: Hilvert
authors: W W
authors: WW
authors: Cleland
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002247:Carbon Isotopes; D002384:Catalysis; D020134:Catalytic Domain; D019277:Entropy; D004789:Enzyme Activation; D007700:Kinetics; D017015:Methanococcales / Q000201:enzymology* / Q000235:genetics; D011302:Prephenate Dehydratase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013912:Threonine / Q000737:chemistry
chemical_list: D019843:Archaeal Proteins; D002247:Carbon Isotopes; D011994:Recombinant Proteins; D013912:Threonine; D011302:Prephenate Dehydratase