Subcellular Localisation and Identification of Superoxide Dismutase in the Leaves of Higher Plants

Abstract

The subcellular location of superoxide dismutase [EC 1.15.1.1] in the leaves of spinach [Spinacia oleracea] and other C3 plants [Hordeum sp. and Medicago sativa] was investigated. Most activity appeared to be located within chloroplasts. These organelles contain a cyanide-sensitive (Cu-Zn) superoxide dismutase, most of which is located in the stroma although some is bound to the thylakoids. Intact chloroplast fractions also contain a cyanide-insensitive (Mn) superoxide dismutase, but this activity is located on the outside of the chloroplasts and may be adsorbed onto them during isolation. Leaf mitochondrial fractions contain only a small percentage of total leaf superoxide dismutase activity, but there is more than can be accounted for by contamination with chloroplasts. Mitochondria contain both a cyanide-sensitive dismutase, apparently located in the intermembrane space, and a cyanide-insensitive activity, apparently located in the matrix. The microsomal fraction contains no superoxide dismutase activity.