Domains of the ! chain

Three functional and structural domains can be
distinguished in all globin chains. They correspond
to the three exons of the gene. Two
domains, consisting of amino acids 1–30 and
105–146 (coded for by exons 1 and 3), are located
on the outside. They are mainly formed of
hydrophilic amino acids. A third domain, lying
inside the molecule (coded for by exon 2), contains
the oxygen-binding site and consists
mainly of nonpolar hydrophobic amino acids.
The amino acid sequences of the hemoglobins
of more than 60 investigated species are identical
in nine positions. These invariant positions
are especially important for the function of the
molecule. Changes (mutations) in the invariant
positions affect function so severely that they
are not tolerated.