ON THE COORDINATION AND OXIDATION-STATES OF THE ACTIVE-SITE COPPER-ION IN PROKARYOTIC CU,ZN SUPEROXIDE DISMUTASES

The active-site copper ion of the prokaryotic Cu,Zn superoxide dismuta se from P. leiognathi is found to undergo reversible reduction upon ir radiation of the protein solution with a high-intensity X-ray beam fro m a third-generation synchrotron source. The same phenomenon is observ ed for the enzyme crystals, whose diffraction pattern has been obtaine d from synchrotron sources. In this case the active-site copper-ligand coordination bond lengths and in particular the Cu-NE2(His61) distanc e are consistent with a copper ion in the reduced state. These results are in line with previous studies on the eukaryotic Cu,Zn superoxide dismutases and suggest the conservation of an identical catalytic mech anism in both the prokaryotic and eukaryotic enzymes. (C) 1998 Academi c Press.