Human oxyHb. View down the twofold symmetry axis. OxyHb's quaternary structure differs from that of deoxyHb in two ways: rotation of one alpha-beta dimer with respect to the other closes the central channel, and the beta subunits come in contact with each other.
  The beta subunits are still related by rotational symmetry in oxyHb, as are the alpha subunits.
  Toggle spacefill. Rotation of one alpha-beta dimer with respect to the other stops when the beta subunits come in contact.
  Toggle rotation of beta subunits as the tetramer shifts from the deoxy to the oxy conformation and back. The position of the iron atom on the left is held constant. Upon oxygen binding the beta subunit on the right rotates towards you. The C-termini are shown in red.
        Note the change in conformation of the last four C-terminal residues. This slight change in conformation is the direct result of the movement of the iron atom upon oxygen binding. In turn, the movement of the C-termini allows the ab dimers to move in a scissor-like fashion as the quaternary structure alternates between the deoxy and oxy conformations.
        The conformational changes at the C-termini are explored in detail in the section.