Subcellular Location of Superoxide Dismutase in Spinach Leaves and Preparation and Properties of Crystalline Spinach Superoxide Dismutase

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Abstract
Localization of superoxide dismutase in spinach chloroplasts was demonstrated by differential and sucrose‐density centrifugations. About half to two thirds of the enzyme in chloroplasts was released by osmotic shock. In peroxisomes, no superoxide dismutase was detected. Disc electrophoresis of chloroplast and supernatant fractions revealed a single band of superoxide dismutase activity corresponding to the purified enzyme. Superoxide dismutase was purified from spinach leaves and prepared in a crystalline state. s020, w was 2.75 S and the molecular weight was approximately 32000 daltons. The enzyme was composed of two subunits of equal size and contained 2 atoms of copper and 2 atoms of zinc per molecule. In addition, visible and ultraviolet spectra, electron paramagnetic resonance spectrum and amino acid composition were similar to these properties of the enzyme isolated from mammalian tissues, Neurospora, green pea and yeast. A possible function of superoxide dismutase in chloroplasts is discussed.