The effective molarity of the substrate phosphoryl group in the transition state for yeast OMP decarboxylase |
| |
Authors: | Sievers Annette Wolfenden Richard |
| |
Institution: | Department 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. |
| |
Keywords: | OMP OMP decarboxylase ODCase Orotidine Connectivity effect Effective molarity Transition state Binding discrimination |
本文献已被 ScienceDirect PubMed 等数据库收录! |
|