Structural Comparison of the Hemoglobins of the Genus Equus with Those of Ruminants

Abstract

Abstract The hemoglobin structures from domestic horse, tarpan horse, and przewalski's horse, donkey, and four subspecies of zebra are compared by peptide mapping and specific staining, with limited isolation of peptides followed by amino acid analysis. Peptide mapping techniques are used to indicate the between phenylalanine and tyrosine at amino acid position α-24 in domestic horse. Such ambiguity at this position cannot be found in the α chain of 51 donkey hemoglobin samples, and is not evident in other equine species. Comparison of the hemoglobin polypeptide chains of the equine family reveals striking similarity among the β chains and a limited number of differences among the α chains. The number of amino acid interchanges accounting for species differences in the α chain are small in contrast to the numerous differences occurring in the α chains of the ruminants. Serine is present at position α-15 in the horse, donkey, and Hartmann's zebra hemoglobins, whereas glycine is present at α-15 in all the other zebra subspecies studied. The limited structural differences in the equine genus are contrasted to the recently reported variations which account for the polymorphic hemoglobins of ruminants. The genetic control of the hemoglobins of the horse, based upon three pairs of alleles for the two different α and single β chains is proposed and compared to a nonallelic scheme for sheep hemoglobins. The numerous evolutionarily effective amino acid substitutions seen in ruminant hemoglobins as compared to other species are accentuated by this comparison within the genus Equus.