page_title: Nickel superoxide dismutase
section_title: Structure
hierarchical_section_title: Nickel superoxide dismutase / Structure
caption_attribution_description: English: SwissPDB viewer rendering of Ni-SOD with the nickel cofactors and nickels binding hooks highlighted.
context_page_description: Nickel superoxide dismutase is a metalloenzyme that, like the other superoxide dismutases, protects cells from oxidative damage by catalyzing the disproportionation of the cytotoxic superoxide radical to hydrogen peroxide and molecular oxygen. Superoxide is a reactive oxygen species that is produced in large amounts during photosynthesis and aerobic cellular respiration. The equation for the disproportionation of superoxide is shown below:
  Ni-SOD was first isolated in 1996 from Streptomyces bacteria and is primarily found in prokaryotic organisms. It has since been observed in cyanobacteria and a number of other aquatic microbes.
  Ni-SOD is homohexameric, meaning that it has six identical subunits. Each subunit has a single nickel containing active site. The disproportionation mechanism involves a reduction-oxidation cycle where a single electron transfer is catalyzed by the Ni²⁺/Ni³⁺ redox couple. Ni-SOD catalyzes close to the barrier of diffusion.
context_section_description: Ni-SOD is a globular protein and is shaped like a hollow sphere. It is homohexameric, meaning that it is made up of six identical subunits. Each subunit is a bundle of four right-handed α-helixes and has a molecular mass of 13.4 kDa (117 amino acids). The subunits align to give Ni-SOD a three-fold axis of symmetry. There are six nickel cofactors in total (one for each subunit). The subunits also have a hydrophobic core, which helps drive protein folding. The core is made up of 17 aliphatic amino acids.
caption: Swiss PDB Viewer rendering of nickel superoxide dismutase with the nickel cofactors shown in blue and the nickel binding hooks shown in green. The six active sites are located in the nickel binding hooks.[5]
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