Porcine superoxide dismutase. Isolation and characterization of a relatively basic cuprozinc enzyme

A cuprozinc superoxide dismutase has been isolated from pig liver. The enzyme is similar to previously described cuprozinc superoxide dismutases in that it is a dimer of about 32 000 molecular weight consisting of approximately two equally sized subunits, and 2 atoms of copper and two atoms of zinc per molecule. It differs, however, from previously described cuprozinc superoxide dismutases because of its higher isoelectric point; pI 6.8 vs 4.9 for bovine enzyme. The diffusion coefficient for the porcine enzyme was determined to be 7.53 x 10(-7) cm2 s-1, while the equivalent spherical hydrodynamic radius was computed as 28.5 A. The enzyme was observed to undergo self-association with time. Sulfhydryl interaction is postulated to be involved.