Characterization of an ironâcontaining superoxide dismutase from a higher plant, Citrus limonum
1994
Almansa, Maria S. | Rio, Luis A. | Sevilla, Francisca
An ironâcontaining superoxide dismutase (SOD, EC 1.15.1.1) was fully characterized from leaves of the higher plant Citrus limonum R. cv. Verna. This enzyme is the first ironâcontaining SOD to be characterized in the plant family Rutaceae. The purified FeâSOD has a molecular mass of about 47 kDa and is composed of two nonâcovalently joined equal subunits. The amino acid composition determined for the enzyme was compared with that of a wide range of SODs and had highest degree of homology with the FeâSODs from Brassica campestris and Nuphar luteum. The enzyme was more labile at high temperatures than some eucaryotic and procaryotic FeâSODs. It showed a maximum stability at pH 7.8. The sensitivity of the enzyme to cyanide, hydrogen peroxide and oâphenanthroline was similar to those reported for other FeâSODs. but the lemon enzyme was comparatively resistant to H2O2. By kinetic competition experiments, the rate constant for the disproportionation of superoxide radicals by lemon FeâSOD was found to be 1.9 × 109M−1 s−1 at pH 7.8 and 25°C. A comparative study between the molecular properties of this higher plant FeâSOD and SODs from different origins is presented.
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