A secondary kinetic isotope effect study of the 1-deoxy-D-xylulose-5- phosphate reductoisomerase-catalyzed reaction: Evidence for a retroaldol-aldol rearrangement

Jeffrey W. Munos, Xiaotao Pu, Steven O. Mansoorabadi, Hak Joong Kim, Hung Wen Liu

Research output: Contribution to journalArticle

51 Citations (Scopus)

Abstract

1-Deoxy-D-xylulose 5-phosphate (DXP) reductoisomerase (DXR, also known as methyl-D-erythritol 4-phosphate (MEP) synthase) is a NADPH-dependent enzyme, which catalyzes the conversion of DXP to MEP in the nonmevalonate pathway of isoprene biosynthesis. Two mechanisms have been proposed for the DXR-catalyzed reaction. In the ,-ketol rearrangement mechanism, the reaction begins with deprotonation of the C-3 hydroxyl group followed by a 1,2-migration to give methylerythrose phosphate, which is then reduced to MEP by NADPH. In the retroaldol/aldol rearrangement mechanism, DXR first cleaves the C3-C4 bond of DXP in a retroaldol manner to generate a three-carbon and a two-carbon phosphate bimolecular intermediate. These two species are then reunited by an aldol reaction to form a new C-C bond, yielding an aldehyde intermediate. Subsequent reduction by NADPH affords MEP. To differentiate these mechanisms, we have prepared [3-2H]- and [4-2H]-DXP and carried out a competitive secondary kinetic isotope effect (KIE) study of the DXR reaction. The normal 2° KIEs observed for [3-2H]- and [4-2H]-DXP provide compelling evidence supporting a retroaldol/aldol mechanism for the rearrangement catalyzed by DXR, with the rate-limiting step being cleavage of the C3-C4 bond of DXP.

Original languageEnglish
Pages (from-to)2048-2049
Number of pages2
JournalJournal of the American Chemical Society
Volume131
Issue number6
DOIs
Publication statusPublished - 2009 Feb 18
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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