Isolation and Characterization of an Iron-containing Superoxide Dismutase from Tomato Leaves, Lycopersicon Esculentum

A cyanide-insensitive superoxide dismutase was purified from tomato leaves (Lycopersicon esculentum, Mill., var. Venture) to apparent homogeneity. The enzyme had twofold higher specific activity (about 4000 standard units) than ferric superoxide dismutases purified from Brassica campestris [Salin, M. L. and Bridges, S. M. (1980) Arch. Biochem. Biophys. 201, 369-374] and Nuphar luteum [Salin, M.L. and Bridges, S. M. (1982) Plant Physiol. 69, 161-165]. The protein had a relative molecular mass of about 42000 and was composed of two equal subunits noncovalently joined. It was negatively charged (pI = 4.6) and contained about 1.45 mol Fe/mol dimer and negligible amounts of Mn, Cu and Zn. Absorption spectrum and sensitivity to NaN3, H2O2 and temperature are also reminiscent of other ferric superoxide dismutases. Comparison of amino acid composition indicated, however, a closer relationship to the Mn-containing enzymes rather than to other Fe-containing superoxide dismutases. Two possible ways of Fe-containing superoxide dismutase acquisition by vascular plants were suggested.