AbstractThe amino acid compositions of homologous tryptic peptides, as well as the amino acid sequences of complete peptide chains, are compared in hemoglobins of different species. Special attention is given to the analyses of mammalian and fish hemoglobins. The multiplicity of hemoglobins in one species and the differences between the hemoglobins of different species are considered. These differences are discussed in view of base exchanges, deletions, insertions, and gene duplications.Enormous differences are found between any two single hemoglobin chains. The number of amino acids varies from 127 to 156 residues. In comparing all the hemoglobins, only eight amino acids are found in identical positions (invariant residues). All hemoglobins analyzed to date follow the rule of “isopolar substitution” of Perutz, Kendrew, and Watson. The results are summarized and considered with regard to certain parallels in the morphol