Superoxide dismutase from the Archaebacterium Thermoplasma acidophilum

Thermoplasma acidophilum is a mycoplasma-like thermophilic organism that has been classified with the archaebacteria. It has a single superoxide dismutase (superoxide : superoxide oxidoreductase, EC 1.15.1.1) which is composed of four identically sized subunits. It has a metal content per molecule of two atoms of iron and probably one of zinc and a molecular weight of 82 000. The amino acid composition is rich in tryptophan and is typical of the manganese or iron superoxide dismutases found in other prokaryotes. However, the enzyme is resistant to denaturation by chloroform plus ethanol, by sodium dodecyl sulfate plus urea or by heat. In these respects it resembles the copper-zinc superoxide dismutase of eukaryotes. It is suggested that the enzyme may belong to a new group of superoxide dismutases.