Abstract
An iron-containing superoxide dismutase has been purified from the protozoan Tetrahymena pyriformis. It has a molecular weight of 85,000 and is composed of four subunits of equal size. The tetramer contains 2.5 g atoms of ferric iron. Visible absorption and electron spin resonance spectra closely resemble those of other iron-containing superoxide dismutases. The amino acid sequence of the iron superoxide dismutase was determined. Each subunit is made up of 196 residues, corresponding to a molecular weight of 22,711. Comparison of the primary structure with the known sequences of other iron-containing superoxide dismutases reveals a relatively low degree of identity (33-34%). However, a higher percentage identity is found with mammalian manganese-containing superoxide dismutases (41-42%). The amino acid sequence is discussed in consideration of residues that may distinguish iron from manganese or dimeric from tetrameric superoxide dismutases.
Highlights
PugetjY, Patrice DurosayQ(j, di Scienze Biochimiche and Centro di Biologia Molecolare de1 Consiglio Nazionale delle Ricerche, Piazzale Aldo Moro 5, 00185 Roma, Italy and the §Institut de Biologie, 13 rue P. et M
In the present study we present the purification and characterization of this tetrameric form of iron superoxide dismutase from the eukaryote Tetrahymenapyriformis
An iron containing superoxide dismutase has been isolated from T. pyriformis
Summary
91 rue de la Croix Nivert, 75015 Paris, France. Mol&culaire, 91190 Gifsur-Yvette, France. ** Present address: Institut Curie, Orsay, France. $$ Present address: Labeaume, 07120 Ruoms, France. A second group of iron enzymes with a molecular weight of about BO,OOO-90,000, consisting of four equal subunits and with 2-4 g atoms of iron has been described. This form of superoxide dismutase has been isolated from three prokaryotes, Mycobacterium tuberculosis [16] and the strict anaerobe archaebacteria Thermoplasma acidophilum [17] and Methanobacterium bryantii [18]. Whereas the evolutionary significance of the nature of the metal (iron, manganese, or copper) at the active center seems relatively clear with respect to a hierarchy (in the order given) of superoxide dismutases, the sense of dimeric or tetrameric forms of the iron (or manganese) enzymes is unknown. No copper-zinc SOD has so far been detected or isolated in lower eukaryotes, this form of SOD is present in the prokaryote Photobacterium leiognathi [19], Caulobacter crescentus [20], and some pseudomonads [21]
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