184.108.40.206 - Superoxide dismutase
There are no alternative names for this Enzyme
2 H(+) + 2 superoxide = H2O2 + O2
Fe cation or Mn(2+) or (Zn(2+) and Cu cation).
In higher organisms, superoxide anions are produced as an occasional byproduct during the one-electron reduction of dioxygen in respiration and photosynthesis. Superoxides are also produced by macrophages as a part of the immune response. Excess amounts of superoxides can inactivate enzymes with iron-sulphur clusters and can lead to the formation of highly oxidising species that can damage cellular constituents. Therefore, organisms must have ways to regulate the concentration of superoxide concentrations. Many Gram-negative bacterial pathogens also possess CuZnSOD to counteract the phagocyte superoxide burst from their hosts.
Zn(II) bound to His63 ND1 raises the pKa of NE2 to ~13, so that unliganded NE2 will always be protonated at physiological pH.
|AA||Uniprot||Uniprot Resid||PDB||PDB Resid|
native state of enzyme regenerated, coordination to a metal ion, native state of cofactor regenerated, radical termination, cofactor used, proton relay, electron transfer, proton transfer
In the resting state of the enzyme, there is a water coordinated to the copper, analogous to the final state of this step, save that the histidine in the resting state is negatively charged and bound to the copper II ion. The superoxide gives up its electron to the Copper II ion. Dioxygen, no longer charged and electrostatically attracted to Arg143, diffuses out of the active site channel, and it is replaced by a water molecule, which starts of as a oxonium and concurrently gives up its proton to the His63, which breaks the histidine bridge [PMID:10026301
The second superoxide molecule enters the active site cavity, displaces a water molecule and hydrogen bonds with the protonated NE2 atom of His63 and a water molecule. A chain of water molecules can relay protons to the active site, replenishing those delivered to form peroxide. The neutral hydrogen peroxide is displaced from the active site by a water molecule to return the enzyme to its initial resting state
Organism KM Value [mM] Substrate Comment Solanum lycopersicum 0.0016 riboflavin Psidium guajava 2.3 riboflavin Bos taurus 0.355 O2- Avicennia marina 0.0115 superoxide pH 8.2, 22°C
Organism Temperature Range Comment Stemona tuberosa 0 - 50 activity range Pseudoalteromonas sp. ANT506 0 - 50 activity range, 13.9% of maximal activity at 0°C, 25.7% at 10°C Curcuma aromatica 0 - 80 activity range between -10-80°C Caragana jubata 0 - 80 activity range between -10-80°C Ulva linza 0 - 35 maximal enzyme activity at 35°C, and 29.8% relative activity at 0°C
Organism pH Range Comment Rhodotorula mucilaginosa 1 - 11 activity range, 75% of maximal activity at pH 1.0, 45% at pH 11.0, profile overview Cristaria plicata 2 - 9 activity range, the enzyme shows 30% of maximal activity at pH 10.0 and is inactive at pH 11.0 Danio rerio 2.2 - 11.2 high enzyme activity Stemona tuberosa 3 - 10 70% of maximal activity within this range Sonneratia alba 3 - 7 high activity range
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