Abstract
The levels of superoxide dismutase (SOD) activity in extracts of preclimacteric apple, banana, avocado and tomato fruits [Lycopersicon esculentum, Pyrus malus, Persea gratissima and Musa sapientum] were not greatly different than in extracts of postclimacteric fruits. Apparently no major quantitative change in SOD occurs in fruits with or preceding the onset of senescence. Tomato fruit SOD was studied in more detail and was found largely in the soluble fraction, and to a lesser extent in the mitochondrial and plastid fractions. The soluble fraction was purified by ammonium sulfate fractionation, column chromatography and isoelectric focusing. Isoelectric focusing separated SOD from contaminating peroxidases. The purified tomato SOD showed an apparent MW of 31,500 determined by gel filtration. Polyacrylamide gel electrophoresis of this preparation indicated 2 SOD components corresponding to 2 protein bands, 1 of which stained more intensely than the other. The purified tomato enzyme was inhibited 90% by 1 mM KCN.