Orotidine 5 -monophosphate decarboxylase ODCase

Abstract An energy decomposition scheme is presented to elucidate the importance of the change of protein conformation substates to the reduction of activation barrier in an enzyme-catalyzed reaction. The analysis is illustrated by the reaction of orotidine 5 -monophosphate decarboxylase (ODCase), in which the catalyzed reaction is at least 10 faster than the spontaneous reaction. Analysis reveals that the enzyme conformation is more distorted in the reactant state than in the transition state. The energy released from conformational relaxation of the protein is the main source of the rate enhancement. The proposed mechanism is consistent with results from site-directed mutagenesis where mutations remote from the reaction center affect kcat but not Kyi. 

The anticancer nucleoside Gemcitabine as its monophosphate derivative (3) has been modified by conjugation of squalene at the N4-position. Using a combination of cryo-EM and SAXS it was shown that the squalenoyl derivative exists as a unilamellar liposome, and that the nanoassembly exhibited enhanced activity compared with Gemcitabine in a resistant cell line." Various C6-modified 2 -deoxy-2 -fluoro-dUMP derivatives have been prepared as potential inhibitors of orotidine 5 -monophosphate decarboxylase (ODCase) of these, the most potent analogue was the 6-iodo-derivative which was found to covalently inhibit ODCase. Aminoacyl-tRNAs... 

How can an enzyme that apparently does not utilize cofactors or covalent intermediates be one of the most proficient enzymes known This is the mystery of orotidine monophosphate decarboxylase (ODCase). In this volume, experts in the field of enzyme catalysis describe their efforts to understand this puzzling enzyme. 

Orotidine S -monophosphate decarboxylase (ODCase) is a key enzyme in the biosynthesis of nucleic acids, effecting the decarboxylation of orotidine 5 -monophosphate (OMP, 1) to form uridine S -monophosphate (UMP, 2, Scheme l).1,2 The conversion of OMP to UMP is biomechanistically intriguing, because the decarboxylation appears to result, uniquely, in a carbanion (3, mechanism i, Scheme 2) that cannot delocalize into a it orbital.3,4 The uncatalyzed reaction in solution is therefore extremely unfavorable, with a AG of... 

The mechanism of the enzymatic decarboxylation of orotidine 5 -mono-phosphate (OMP) to uridine 5 -monophosphate (UMP) (see Fig. 1) is an intriguing problem for which many solutions have been offered. Even before 1995 when Wolfenden and Radzicka declared OMP decarboxylase (ODCase) to be the most proficient enzyme [1], several different mechanisms had been proposed. Since that time, other mechanisms have been advocated. Curiously, the appearance of crystal structures for various wild-type and mutant ODCases has led not to a definitive picture of catalysis, but to even more conjecture and controversy concerning the mechanism. 

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