Journal
BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS
Volume 1804, Issue 4, Pages 752-754Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbapap.2009.11.018
Keywords
Prephenate dehydratase; C-13 Isotope effect; Transition state structure
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Funding
- ETH Zurich
- Swiss National Science Foundation
- NIH [GM18938]
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R37GM018938, R01GM018938] Funding Source: NIH RePORTER
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The C-13 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. (C) 2009 Elsevier B.V. All rights reserved.
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