Occurrence of Cu,Zn-Superoxide Dismutase in the Intrathylakoid Space of Spinach Chloroplasts

Thylakoids obtained from intact spinach chloroplasts showed no superoxide dismutase (SOD) activity, but Cu,Zn- and Mn-SOD activities were detected in the presence of Triton X-100. Thylakoid membranes and the lumen fraction were separated by centrifugation after treatment of the thylakoids with a Yeda pressure cell. Cu,Zn-SOD was found in the lumen fraction. Mn-SOD was detected in the thylakoid fraction only after addition of 1% Triton X-100. Antibody against spinach Cu,Zn-SOD did not interact with the latent Cu,Zn-SOD in the thylakoids unless Triton was added. These results indicate that Cu,Zn-SOD occurs in the lumen in addition to the stroma of spinach chloroplasts, and Mn-SOD binds to the thylakoid membranes.