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FEBS Lett. 2006 Feb 20;580(5):1485-9. Epub 2006 Feb 2.

Extracellular superoxide dismutase exists as an octamer.

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Center for Insoluble Protein Structures (inSPIN), Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark.


Human extracellular superoxide dismutase (EC-SOD) is involved in the defence against oxidative stress induced by the superoxide radical. The protein is a homotetramer stabilised by hydrophobic interactions within the N-terminal region. During the purification of EC-SOD from human aorta, we noticed that material with high affinity for heparin-Sepharose formed not only a tetramer but also an octamer. Analysis of the thermodynamic stability of the octamer suggested that the C-terminal region is involved in formation of the quaternary structure. In addition, we show that the octamer is composed of both aEC-SOD and iEC-SOD folding variants. The presence of the EC-SOD octamer with high affinity may represent a way to influence the local concentration of EC-SOD to protect tissues specifically sensitive to oxidative damage.

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