Phosphate ester hydrolysis is catalyzed by a bacterial transferrin: potential implications for in vivo iron transport mechanisms.

Two synergistic anions, p-nitrophenyl phosphate ester (NPP)andSO42-, were found to form new stable assemblies with Fe3+ and a bacterial transferrin, FbpA (FbpA=ferric binding protein). Fe3+FbpA–SO4 undergoes rapid anion exchange in the presence of NPP to form Fe3+FbpA–NPP. Formation of Fe3+FbpA–NPP was found to accelerate the rate of hydrolysis of the bound phosphate ester (khyd=1.6×10−6 s−1 at 25 °C and pH 6.5) by >103 fold over the uncatalyzed reaction. These findings suggest a dual function for FbpA in vivo: transport of Fe3+ across the periplasmic space to the inner membrane in certain gram-negative bacteria and hydrolysis of periplasmic polyphosphates.