Article ID Journal Published Year Pages File Type
10582861 Bioorganic Chemistry 2005 8 Pages PDF
Abstract
The second order rate constant (kcat/Km) for decarboxylation of orotidine by yeast OMP decarboxylase (ODCase), measured by trapping 14CO2 released during the reaction, is 2 × 10−4 M−1 s−1. This very low activity may be compared with a value of 3 × 107 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 (Ki = 7 × 10−4 M), imply an effective concentration of 1.1 × 109 M for the substrate phosphoryl group in stabilizing the transition state for enzymatic decarboxylation of OMP. The observed difference in rate (1.5 × 1011-fold) is the largest effect of a simple substituent that appears to have been reported for an enzyme reaction.
Related Topics
Physical Sciences and Engineering Chemistry Organic Chemistry
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