OMP decarboxylase: an experimental test of electrostatic destabilization of the enzyme-substrate complex.

6-Methylaminouridine 5'-phosphate (MAUMP) inhibits OMP decarboxylase (Ki = 3 x 10-6 M) maximally at pH values where its amino group is uncharged. Comparison of the chemical shift of free [7-13C]-MAUMP in solutions of varying pH, with that of the enzyme-bound species confirms that this inhibitor is bound with its amino group uncharged. This enzyme's apparent lack of affinity for a cationic substituent, located near the position that would ordinarily be occupied by the scissile carboxylate group of the substrate, does not appear to support the view that the E-S complex is destabilized by electrostatic repulsion in the ground state.