Amino Acid Sequence of the Cytochrome c from the Dogfish, Squalus sucklii

Cytochrome c was isolated in pure form from hearts of the Puget Sound dogfish, Squalus sucklii. The protein was digested with chymotrypsin, and the resulting peptide fractions were resolved by ion exchange chromatography on Dowex 50 with volatile buffers. The peptides were purified by chromatography or electrophoresis on paper and the sequences were determined. By comparing the peptides with the sequences of other vertebrate cytochromes c, the complete sequence of 104 residues was deduced. Dogfish cytochrome c differs from that of the tuna in 17 or 19 residues, including the deletion, from the chicken and rattlesnake in 18 residues, and from the human in 23 residues. Certain amino acid replacements of both tuna and dogfish cytochromes c are common to the two species of fish and distinguish them from other vertebrate cytochromes.