STRUCTURE OF DEOXY-QUATERNARY HEMOGLOBIN WITH LIGANDED BETA-SUBUNITS

We have determined the structure of a T-state haemoglobin in which the haem groups of the β subunits have carbon monoxide bound, and the α subunits have nickel replacing the haem iron and are ligand-free. The structural adjustments on binding ligand in the T state are in the same direction as those associated with the quaternary transition, and a translational shift of the haem is severly restricted. We explain how these observations may account for the low ligand affinity of the β haem of T-state haemoglobin. © 1990 Academic Press Limited.