Iron superoxide dismutases: structure and function of an archaic enzyme.

Iron and manganese superoxide dismutases are phylogenetically closely related. They are compared by in silico analysis with regard to their metal specificity and their three-dimensional structure. Special attention is given to the structure and properties of superoxide dismutases from archaeal prokaryotes. The mechanism and the extreme thermostability of superoxide dismutase from Sulfolobus acidocaldarius are discussed on the basis of its high-resolution X-ray structure. An alternating-site mechanism and an evolutionary origin of superoxide dismutases under the environmental conditions on the early Earth are proposed.