Comparison of properties between human recombinant and placental copper-zinc SOD

The physicochemical properties of purified recombinant human copper-zinc superoxide dismutase (r-hSOD) were compared with those of human placental copper-zinc superoxide dismutase (h-SOD). No differences were found in specific activity, metal contents, amino acid composition, and tryptic peptide map. The spectrophotometric properties including UV, ESR, and CD spectra were also similar. The result of isoelectric gel electrophoresis showed that the difference in isoelectric point (pI) was derived from acetylation of the N-terminal amino acid (alanine) in h-SOD. In SDS-polyacrylamide gel electrophoresis, both SODs showed the same behavior and enzymic activity was retained only under non-reducing conditions. ESR analysis of the denatured enzyme suggested that the high stability was derived from the structure of the active site around copper. Experiments using other metal-substituted SODs (Cu, Co in place of zinc) suggested that zinc contributed to the stability and the unique electrophoretic behavior of the enzyme.