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 periplasmic space of an Escherichia coli strain unable to synthesize MnSOD and FeSOD. Gel filtration chromatography evidenced that under all the experimental conditions tested the enzyme was monomeric. The catalytic activity of this CuZnSOD was comparable to that of other well characterized dimeric eukaryotic isoenzymes, indicating that a dimeric structure is not essential to ensure enzymatic efficiency. Furthermore the purified enzyme proved to be highly heat-stable and, uniquely among CuZnSODs, protease-sensitive. The latter property may explain the previously described lability of this protein in cell extracts.