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Updated: Aug 13, 2026

Steady-state, Pre-steady-state, and Single-turnover Kinetic Measurement for DNA Glycosylase Activity
Published on: August 19, 2013
The effective molarity of the substrate phosphoryl group in the transition state for yeast OMP decarboxylase
Annette Sievers1, Richard Wolfenden
1Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599-7260, USA.
Abstract:
The second order rate constant (k(cat)/K(m)) for decarboxylation of orotidine by yeast OMP decarboxylase (ODCase), measured by trapping (14)CO(2) released during the reaction, is 2 x 10(-4)M(-1)s(-1). This very low activity may be compared with a value of 3 x 10(7)M(-1)s(-1) for the action of yeast OMP decarboxylase on the normal substrate OMP. Both activities are strongly inhibited by 6-hydroxy UMP (BMP), and abrogated by mutation of Asp-96 to alanine. These results, in conjunction with the binding affinity of inorganic phosphate as a competitive inhibitor (K(i)=7 x 10(-4)M), imply an effective concentration of 1.1 x 10(9)M for the substrate phosphoryl group in stabilizing the transition state for enzymatic decarboxylation of OMP. The observed difference in rate (1.5 x 10(11)-fold) is the largest effect of a simple substituent that appears to have been reported for an enzyme reaction.
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