PURIFICATION AND SUBUNIT STRUCTURE OF EXTRACELLULAR-SUPEROXIDE DISMUTASE FROM MOUSE LUNG-TISSUE

The first purification of mouse extracellular superoxide dismutase (EC -SOD) and the analysis of the native enzyme are described. Mouse EC-SO D was purified from lung tissues with a high recovery (41%) and a spec ific polyclonal antibody against the purified enzyme was obtained. The purified enzyme had a strong affinity for heparin and a molecular mas s of 150 kDa (estimated by a gel filtration chromatography). The nativ e mouse EC-SOD was composed of two different sizes of subunits, a M-r of 33 and 35 kDa (determined by SDS-PAGE). The 35-kDa subunit had an i nterchain disulfide bond at the C-terminus and existed as a covalent d imer in the molecule, whereas the 33-kDa subunit resulted from the 35- kDa subunit by truncating its C-terminus as a posttranslational modifi cation, with resultant loss of the interchain disulfide bond. These re sults suggest that the native mouse EC-SOD is a heterotetramer compose d of two different dimers, with or without a covalent bond. (C) 1997 A cademic Press.