THE CU,ZN SUPEROXIDE-DISMUTASE FROM ESCHERICHIA-COLI RETAINS MONOMERIC STRUCTURE AT HIGH-PROTEIN CONCENTRATION - EVIDENCE FOR ALTERED SUBUNIT INTERACTION IN ALL THE BACTERIOCUPREINS

Gel-filtration chromatography experiments performed at high protein co ncentrations demonstrate that the Cu,Zn superoxide dismutase from Esch erichia coli is monomeric irrespective of the buffer and of ionic stre ngth. The catalytic activity of the recombinant enzyme is comparable w ith that of eukaryotic isoenzymes, indicating that the dimeric structu re commonly found in Cu,Zn superoxide dismutases is not necessary to e nsure efficient catalysis. The analysis of the amino acid sequences su ggests that an altered interaction between subunits occurs in all bact erial Cu,Zn superoxide dismutases. The substitution of hydrophobic res idues with charged ones at positions located at the dimer interface of all known Cu,Zn superoxide dismutases could be specifically responsib le for the monomeric structure of the E. coli enzyme.