Investigation of the active site of Escherichia coli Cu,Zn superoxide dismutase reveals the absence of the copper-coordinated water molecule. Is the water molecule really necessary for the enzymatic mechanism?

The active site of the Cu,Zn superoxide dismutase from Escherichia coli in the oxidized Cu(II) state has been studied by nuclear magnetic relaxation d ispersion (NMRD), optical and nuclear magnetic resonance spectroscopy. The orientation of some metal ligands is different with respect to all the othe r Cu,Zn superoxide dismutases. Moreover, NMRD measurements demonstrate the lack of a copper-coordinated water molecule. In spite of these differences the enzymatic activity is still high. Azide also hinds copper with normal a ffinity and induces modifications in the active site comparable to those pr eviously observed in the eukaryotic enzymes. Our results suggest that, in t his enzyme, the copper-coordinated water molecule appears not necessary for the enzymatic reaction. A role for the copper-coordinated water molecule i s discussed in the light of recent crystallographic studies. (C) 2000 Feder ation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.