Cyanide Insensitive Iron Superoxide Dismutase in Euglena gracilis Comparison of the Reliabilities of Different Test Systems for Superoxide Dismutases

Abstract

Abstract Two proteins (P1 and P2 , with mol weights of 57,500 and 27,500, respectively) were isolated from Euglena gracilis. Both proteins show cyanide-insensitive superoxide dismutase activity in the “classical” superoxide dismutase assay, using xanthine-xanthine oxidase as O2·− generator. If O2·− is generated chemically (autoxidation of reduced anthraquinone), photochemically (illuminated riboflavine) or pulse radiolytically, only protein P1 but not P2 shows SOD activity. Protein P1 contains 1 g atom (determined: 0.82) iron (no Mn or Cu) per mole protein and may thus be defined as iron-superoxide dismutase. Protein P2 , showing the spectral properties of a flavoprotein, exhibits the activities of ferredoxin-NADP-oxidoreductase and “diaphorase”. The cyanide-insensitive SOD-activity of this “diaphorase” in the xanthine oxidase-assay for superoxide dismutase makes this classical and commonly used test unreliable for assaying cyanide insensitive SOD activities. The existence of the “prokaryote-type” of superoxide dismutase (Fe-SOD) in Euglena gracilis is exceptional for an eukaryotic, autotrophically grown organisms.