Superoxide dismutase (SOD) is responsible for
the elimination of cytotoxic active oxygen by catalyzing the dismutation
of the superoxide radical to oxygen and hydrogen peroxide. There
are three SOD isoenzymes in mammalian cells. They are: extracellular
SOD (EC SOD), copper and zinc-containing SOD (Cu/Zn SOD) and manganese-containing
SOD (Mn SOD). The Cu/Zn form contains Cu and Zn ions and exists
as a 32 kDa dimer in the cytosol. Mn SOD is an 80 kDa tetramer
that contains Mn ion and resides in the mitochondrial matrix. Mn
SOD is a tumor necrosis factor (TNF)- inducible enzyme that protects
cells from TNF-mediated apoptosis via superoxide anion detoxification
and the subsequent regulation of apoptosis through cytochrome c
release and the modulation of the redox state of the mitochondria.
Mn SOD has also been shown to be a tumor suppressor in human breast
cancer. Overexpression of this enzyme protects neurons from NMDA-
and nitric oxide-induced neurotoxicity.
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