ISOLATION OF AN ACTIVE AND HEAT-STABLE MONOMERIC FORM OF CU,ZN SUPEROXIDE-DISMUTASE FROM THE PERIPLASMIC SPACE OF ESCHERICHIA-COLI

We have purified the Cu,Zn superoxide dismutase (CuZnSOD) from the per iplasmic space of an Escherichia coli strain unable to synthesize MnSO D and FeSOD. Gel filtration chromatography evidenced that under all th e experimental conditions tested the enzyme was monomeric. The catalyt ic activity of this CuZnSOD was comparable to that of other well chara cterized dimeric eukaryotic isoenzymes, indicating that a dimeric stru cture is not essential to ensure enzymatic efficiency. Furthermore the purified enzyme proved to be highly heat-stable and, uniquely among C uZnSODs, protease-sensitive. The latter property may explain the previ ously described lability of this protein in cell extracts.