Properties and primary structure of the cytochrome c from the flight muscles of the moth, Samia cynthia.

The complete amino acid sequence of the cytochrome c from the flight muscles of a saturnid moth, Samia Cynthia, has been established. This protein is functionally and structurally homologous to other mammalian-type cytochromes c. However, it differs from cytochromes c of vertebrate origin by having a nonacetylated NHz-terminal residue, being 107 rather than 104 residues long and carrying an arginine rather than a lysine at Position 13, immediately before the first thioether-bonded cysteine. These characteristics appear to be common to nonvertebrate cytochromes c, including the bakers’ yeast protein. In other primary structure features, S. Cynthia cytochrome c resembles the vertebrate more than the yeast proteins, as might be expected from the phylogenetic relations of fungi, invertebrates, and vertebrates. S. Cynthia cytochrome c carries a phenylalanine at Position 65, in place of the methionyl residue found in the other homologous proteins, indicating the lack of a specific requirement for methionine at this position.