Purification of the cytosolic CuZn-superoxide dismutase (CuZn-SOD) of Marchantia paleacea var. diptera and its resemblance to CuZn-SOD from chloroplasts

Abstract

Suspension-cultured cells of Marchantia paleacea var. diptera contain a single form of CuZn-superoxide dismutase (SOD; EC 1.15.1.1) which is localized in the cytosol. SOD activity was found in cells cultured under heterotrophic, photoheterotrophic and photoautotrophic conditions. The CuZn- SOD was purified to homogeneity from liverwort cells that had been cultured heterotrophically. Its molecular mass was 32.6 kDa, and it contained 17.5 kDa subunits, an indication that the enzyme is a homodimer. The enzyme had peaks of absorption at 252, 258 and 264 nm in the ultraviolet region, due to the presence of phenylalanine, and a peak at 680 nm in the visible region, which is characteristic of CuZn-SODs from chloroplasts. The amino acid sequence of the amino-terminal region of the enzyme exhibited a very high degree of homology to those of chloroplast CnZn-SODs. An antiserum raised against the CuZn-SOD from liverwort cross-reacted more strongly with the enzyme from spinach chloroplasts, than with the enzyme from spinach cytosol. These results indicate that the CuZn-SOD of liverwort resembles CuZn-SOD in chloroplasts even though the former is located in the cytosol.