CONSERVED ENZYME-SUBSTRATE ELECTROSTATIC ATTRACTION IN PROKARYOTIC CU,ZN SUPEROXIDE DISMUTASES

The catalytic activity of wild type Escherichia coli Cu,Zn superoxide dismutases and of two mutants in which two lysine residues conserved i n most bacterial Cu,Zn superoxide dismutases have been replaced by ser ine was investigated by pulse radiolysis and Brownian dynamics simulat ions. Experimental and computational data show that neutralization of Lys60 strongly reduces the catalytic activity of the enzyme (similar t o 50%), indicating that this residue has a primary role in the electro static attraction of the substrate towards the catalytic copper. Neutr alization of Lys63 does not significantly influence the catalytic rate constant. The results suggest that prokaryotic Cu,Zn superoxide dismu tases have evolved an electrostatic mechanism to facilitate the enzyme -substrate encounter that is functionally equivalent to that already f ound in the eukaryotic enzymes. (C) 1998 Academic Press.