Mutation of the Metal‐Bridging Proton‐Donor His63 Residue in Human Cu, Zn Superoxide Dismutase

摘要: The bridging His63 residue in human Cu, Zn superoxide dismutase, which binds both metals, has been replaced by a Cys residue. mutant protein purified from Escherichia coli and appears to be normal dimer. Spectroscopic techniques (electronic spectroscopies, EPR, nuclear magnetic relaxation dispersion) show that Cys63 the zinc ion, but not copper latter is probably five co-ordinated with three histidine ligands two water molecules. reduction potential of ion Cu2+/Cu+ pair decreases 0.41 V 0.27 at neutral pH still remains intermediate between those O2/O2− O2−/H2O2 pairs so can oxidize reduce O2− substrate, requirement for dismutase activity. enzyme substrate-analogue azide (N3−), displaces one molecule, near affinity, whereas activity substrate reduced less than 1 % wild-type levels 7.8. properties are discussed relation superoxide–copper electron transfer process catalytic mechanism.