The Amino-Acid Sequence of Rat Cu-Zn Superoxide Dismutase

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Abstract
The primary structure of Cu-Zn superoxide dismutase isolated from rat liver was detemrined. The enzyme was reduced, carboxy-methylated and fragmented by treatment with cyanogen bromide, trypsin or Staphylococcus aureus proteinase V8. The resulting peptides were separated by gel filtration or high performance liquid chromatography and sequenced by automated Edman degradation. The total sequence of 153 amino-acid residues per subunit was reconstructed from overlapping peptides. Rat Cu-Zn superoxide dismutase proved to be closely related to the corresponding sequences of other mammals in having more than 80% identical amino-acid residues in homologous position and an acetylated N-terminus. Comparison of the rat Cu-Zn superoxide dismutase structure with those of other species suggests (i) a similar phylogenetic distance between rat, man, pig, cattle and horse and (ii) a rapid molecular divergence during vertebrate development compared to earlier evolutionary periods.