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Abstract
A cyanide-insensitive superoxide dismutase was purified to apparent homogeneity from lemon leaves (Citrus limonum R). The enzyme was isolated from leaf extracts by ammonium sulfate salting-out. and ion-exchange, gel filtration and hydroxylapatite column chromatography. The purified Fe-SOD had a specific activity of about 1.500 U/mg and represents approximately 1.6% of the total soluble protein in lemon leaf extracts. A molecular weight of 47,500 was determined for the enzyme. Analytical gel electro-focusing of the purified preparation revealed the presence of two isozymes with pl values of 5.13 and 4.98. Metal analysis showed the presence of I g-atom of iron and 0.5g-atom of manganese per mol of enzyme. The visible and UV absorption spectra of the Citrus enzyme were similar to those reported for other iron-containing SODS from different origins. The significance of the presence of Fe-SOD in higher plants is briefly discussed.