Activation of R235A mutant orotidine 5′-monophosphate decarboxylase by the guanidinium cation: Effective molarity of the cationic side chain of Arg-235

Shonoi A. Barnett, Tina L. Amyes, B. McKay Wood, John Alan Gerlt, John P. Richard

Research output: Contribution to journalArticle


The R235A mutation at yeast orotidine 5′-monophosphate decarboxylase (OMPDC) results in a 1300-fold increase in Km and a 14-fold decrease in kcat for decarboxylation of orotidine 5′-monophosphate, corresponding to a 5.8 kcal/mol destabilization of the transition state. There is strong activation of this mutant enzyme by added guanidinium cation (Gua +): 1 M Gua+ stabilizes the transition state by ca. 3 kcal/mol. This stabilization is due to the binding of Gua+ to the binary Emut·OMP complex, with a Kd of 50 mM, to form the 9-fold more reactive ternary Emut·OMP·Gua + complex. The "effectivemolarity" of the cationic side chain of Arg-235 at the wild-type enzyme is calculated to be 160 M.

Original languageEnglish (US)
Pages (from-to)824-826
Number of pages3
Issue number5
StatePublished - Feb 9 2010


ASJC Scopus subject areas

  • Biochemistry

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