Equilibrium of formation of the 6-carbanion of UMP, a potential intermediate in the action of OMP decarboxylase.
There has been some speculation that the C-6 position in UMP may be unusually acidic, stabilizing a carbanion that is generated at this position during OMP decarboxylation. On the basis of the rate of OH- catalyzed deuterium exchange at elevated temperatures we estimate that the pKa value for ionization at C-6 of dimethyl uracil is 34 +/- 2 in water. The same method yields a value of 37 +/- 2 for ionization at C-2 of thiophene in good agreement with the value determined by polarographic methods. The barrier to proton release (46 kcal/mol) is even higher than that for CO2 release from orotic acid derivatives.
Sievers
Annette
A
Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599-7260, USA.
Wolfenden
Richard
R
D003903:Deuterium / Q000737:chemistry; D006358:Hot Temperature; D007700:Kinetics; D009964:Orotidine-5'-Phosphate Decarboxylase / Q000737:chemistry / Q000378:metabolism*; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D014542:Uridine Monophosphate / Q000737:chemistry / Q000378:metabolism*
D014498:Uracil; C002451:1,3-dimethyluracil; D003903:Deuterium; D014542:Uridine Monophosphate; D009964:Orotidine-5'-Phosphate Decarboxylase