Kinetic mechanism of Plasmodium falciparum hypoxanthine-guanine-xanthine phosphoribosyltransferase

Sourav Roy, Lakshmeesha K. Nagappa, Vasudeva S. Prahladarao, Hemalatha Balaram

Research output: Contribution to journalArticle

6 Scopus citations

Abstract

Plasmodium falciparum hypoxanthine-guanine-xanthine phosphoribosyltransferase (PfHGXPRT) exhibits a kinetic mechanism that differs from that of the human homolog. Human HGPRT follows a steady-state ordered mechanism, wherein PRPP binding precedes the binding of hypoxanthine/guanine and release of product IMP/GMP is the rate limiting step. In the current study, initial velocity kinetics with PfHGXPRT indicates a steady-state ordered mechanism, wherein xanthine binding is conditional to the binding of PRPP. The value of the rate constant for IMP dissociation is greater by 183-fold than the kcat for hypoxanthine phosphoribosylation and this results in the absence of burst in progress curves from pre-steady-state kinetics. Further, IMP binding is 1000 times faster (4 s-1 at 0.5 μM IMP) when compared to the kcat (3.9 ± 0.2 × 10-3 s-1) for the reverse IMP pyrophosphorolysis reaction. These results lend support to the fact that in both forward and reverse reactions, the process of chemical conversion (formation of IMP/hypoxanthine) is slow and the events of ligand association and dissociation are faster.

Original languageEnglish (US)
Pages (from-to)111-120
Number of pages10
JournalMolecular and Biochemical Parasitology
Volume204
Issue number2
DOIs
StatePublished - Dec 1 2015
Externally publishedYes

Keywords

  • IMP pyrophosphorolysis
  • Kinetic mechanism
  • PfHGXPRT
  • Pre-steady-state kinetics
  • Single-turnover

ASJC Scopus subject areas

  • Molecular Biology
  • Parasitology

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