Orotidine 5'-phosphate decarboxylase

Orotidine 5'-phosphate decarboxylase is an enzyme involved in pyrimidine metabolism.

Function
The enzyme converts orotidine monophosphate (OMP) to uridine monophosphate (UMP) by liberating carbon dioxide. It is known for being an extraordinarily efficient catalyst capable of accelerating the uncatalyzed reaction rate by a factor of 1017. To put it in perspective, the enzyme can catalyze the substrate in 18 milliseconds, in a reaction that would take 78 million years to complete without the enzyme.

Unicellular vs Multicellular Function
In yeast and bacteria OMP decarboxylase is a single-function enzyme. However, in mammals, OMP decarboxylase is part of a single protein with two catalytic activities. This bifunctional enzyme is named UMP synthase and it also catalyzes the preceding reaction in pyrimidine nucleotide biosynthesis, the transfer of ribose 5-phosphate from 5-phosphoribosyl-1-pyrophosphate to orotate to form OMP.