Sea snake (Microcephalophis gracilis) hemoglobin: primary structure and relationships to other forms

The hemoglobin of the sea snake Microcephalophis gracilis was purified and the primary structure of the alpha and beta chains determined. This is the first sea snake hemoglobin structure characterized, and apparently also the first complete structure of any snake hemoglobin (an alpha chain of a viper was known), allowing judgments of reptilian variants. Variations between the sea snake form and other reptilian forms are large (52-65 differences for the alpha chains), of similar order as those between the sea snake and avian (56-65 differences) or human (58 differences) forms. Functionally, 19 residues at alpha/beta contact areas and 7 at heme contacts are exchanged in relation to the human alpha and beta chains. Four positions of the sea snake hemoglobin contain residues thus far unique to this form. However, all replacements appear compatible with conserved overall functional properties.