Superoxide dismutases (SODs) are ubiquitous metalloproteins that prevent damage by oxygen-mediated free radicals by catalysing the dismutation of superoxide into molecular oxygen and hydrogen peroxide []. Superoxide is a normal by-product of aerobic respiration and is produced by a number of reactions, including oxidative phosphorylation and photosynthesis. The dismutase enzymes have a very high catalytic efficiency due to the attraction of superoxide to the ions bound at the active site [, ].There are three forms of superoxide dismutase, depending on the metal cofactor: Cu/Zn (which binds both copper and zinc), Fe and Mn types. The Fe and Mn forms are similar in their primary, secondary and tertiary structures, but are distinct from the Cu/Zn form []. Prokaryotes and protists contain Mn, Fe or both types, while most eukaryotic organisms utilise the Cu/Zn type. The Cu/Zn form has an immunoglobulin-like β-sandwich fold.Defects in the human SOD1 gene causes familial amyotrophic lateral sclerosis (Lou Gehrig's disease). Cytoplasmic and periplasmic SODs exist as dimers, whereas chloroplastic and extracellular enzymes exist as tetramers. Structural analysis supports the notion of independent functional evolution in prokaryotes (P-class) and eukaryotes (E-class) [, , , , , , , ].
Superoxide dismutases (SODs) are ubiquitous metalloproteins that prevent damage by oxygen-mediated free radicals by catalysing the dismutation of superoxide into molecular oxygen and hydrogen peroxide []. Superoxide is a normal by-product of aerobic respiration and is produced by a number of reactions, including oxidative phosphorylation and photosynthesis. The dismutase enzymes have a very high catalytic efficiency due to the attraction of superoxide to the ions bound at the active site [, ].There are three forms of superoxide dismutase, depending on the metal cofactor: Cu/Zn (which binds both copper and zinc), Fe and Mn types. The Fe and Mn forms are similar in their primary, secondary and tertiary structures, but are distinct from the Cu/Zn form []. Prokaryotes and protists contain Mn, Fe or both types, while most eukaryotic organisms utilise the Cu/Zn type.Defects in the human SOD1 gene causes familial amyotrophic lateral sclerosis (Lou Gehrig's disease). Cytoplasmic and periplasmic SODs exist as dimers, whereas chloroplastic and extracellular enzymes exist as tetramers. Structural analysis supports the notion of independent functional evolution in prokaryotes (P-class) and eukaryotes (E-class) [, , , , , , , ].
