Abstract
Superoxide dismutase from chicken-liver mitochondria (manganese enzyme) and the two dismutases from Escherichia coli (manganese and iron enzymes) were analyzed through 29 cycles of automated Edman degradations. The high degree of homology among the amino-terminal sequences of these three dismutases corroborates their known similarity of structural and functional properties, and serves as further evidence for the endosymbiotic origin of mitochondria. In contrast, these three sequences exhibit no significant homology with the amino-terminal sequence of bovine-erythrocyte superoxide dismutase, which is consistent with the classification of eukaryotic copper-zinc dismutases as a family distinct from the manganese enzymes in stability and catalytic properties.