Quaternary structure: assembly of multiple polypeptide subunits

    The quarternary structure of hemoglobin comprises two alpha and two beta subunits. The spatial arrangement of each alpha-beta pair is symmetrical. Contacts between the subunits are by means of H-bonds. The heme groups are inorganic iron (Fe++) groups that assist in binding oxygen (O2): they are not a typical part of the quaternary structure of proteins.

Figure © 2000 by Griffiths et al. ; text © 2008 by Steven M. Carr