Taxonomical classification of the guinea pig based on its Cu/Zn superoxide dismutase sequence

Cu-Zn superoxide dismutase was purified from guinea pig (Cavia porcellus) liver up to electrophoretic homogeneity and its amino acid sequence was elucidated by automated Edman degradation of proteolytic fragments and mass spectrometry. The protein was classified as a typical mammalian cytosolic Cu-Zn superoxide dismutase by molecular mass, specific activity, amino acid sequence and N-terminal acetylation. A dendrogram constructed from previously known vertebrate cytosolic Cu-Zn superoxide dismutase sequences reflects the commonly accepted taxonomy and phylogenetic relationships of the species, whereas the guinea pig sequence is similarly remote form muriform rodents, lagomorphs, equiforms and primates. The data appear incompatible with the assumption that the Caviomorpha with the representative Cavia porcellus form a common phylogenetic clade with the muriform rodents but rather have to be considered a distinct order of mammals. The degree of similarity of the sequences further suggests that the mammalian clade diverged into rodents, primates, lagomorphs and caviomorphs at about the same time.