The role of metal ions in phosphate ester hydrolysis

Abstract

Many phosphatases make use of metal ions to aid catalysis of phosphate ester hydrolysis. Here, we investigate the impact of metal ions on the potential energy surface (PES), and hence the preferred reaction mechanism, for a simple model for hydrolysis of phosphate ester monoanions. We show that, while both associative (A_N + D_N) and dissociative (D_N + A_N) mechanisms are represented on the potential energy surfaces both in the presence and absence of metal ions, the D_N + A_N process is favoured when there are no metal ions present and the A_N + D_N process is favoured in the presence of two metal ions. A concerted (A_ND_N) process is also available in the presence of two metal ions, but proceeds via a high-energy transition state. In the presence of only a single metal ion the A_ND_N process is the most favoured, but still proceeds via a high-energy transition state. Thus, we conclude that metallo-enzyme phosphatases are likely to utilise an associative process, while those that function without metal ions may well follow a dissociative process.