The primary structure and functional properties of the hemoglobins of a ground squirrel (Spermophilus townsendii, Rodentia)

The hemoglobin of the ground squirrel Spermophilus townsendii consists of two components which are present in a ratio of ca. 2:1. The two hemoglobins have identical alpha-chains, but differ in their beta-chains. We present the primary structures of the alpha- and the two beta-globin chains. Following chain separation by chromatography on carboxymethyl-cellulose CM-52, the amino-acid sequences were established by automatic Edman degradation of the globin chains and the tryptic peptides, as well as of a peptide obtained by acid hydrolysis of the Asp-Pro bond of the beta-chains. The two beta-chains differ by only one amino-acid residue, Ala being present in the main and Asp in the minor component in position 58 (E2). The comparison with human hemoglobin showed only 14 exchanges in the alpha-chains but 33 in the beta-chains. Whereas no contact positions are affected in the alpha-chains, we found four such substitutions in the beta-chains, including one heme contact, two alpha 1/beta 1-contacts, and one alpha 1/beta 2-contact. It seems however, that the substitution found in the beta-chains has no effect on the oxygen affinity.