The gas phase proton affinity of uracil: measuring multiple basic sites and implications for the enzyme mechanism of orotidine 5'-monophosphate decarboxylase.

We have shown for the first time experimentally that the O2 and O4 sites of uracil have different proton affinities, and as implied in previous computational studies, the O4 is more basic and would be energetically preferred in an orotate ribose 5'-monophosphate decarboxylase catalysis mechanism involving proton transfer to oxygen.