Rabbit Heart Cytochrome c

Abstract The amino acid sequence of rabbit heart cytochrome c has been determined from the complete amino acid sequences of the chymotryptic peptides and the compositions of the tryptic peptides. This primary structure, as well as the properties of the protein, shows that rabbit heart cytochrome c is typically of the mammalian type. The rabbit protein consists of a polypeptide chain 104 residues in length with a clustered distribution of the hydrophobic and basic amino acids similar to that of other cytochromes c of the same group. The numbers of residue differences between the cytochrome c of rabbit and those of a number of mammals are in the range of 4 to 9, while the differences between the rabbit protein and those of chicken, tuna, moth, and bakers' yeast are 8, 18, 27, and 44, respectively. The latter set of variations is compatible with an approximate proportionality between the extent of cytochrome c residue substitutions and the times elapsed since the divergence of the evolutionary lines leading to species in different large taxonomic groupings. The most remarkable variation in the rabbit protein is the replacement of a valine for the proline commonly observed in other cytochromes c in position 44.