Transduction of binding energy into hemoglobin cooperativity

Hemoglobin is a tetrameric molecule consisting of two identical alpha beta dimers which assemble into either of two quaternary structures, T or R. Recent studies on mutant and partially ligated hemoglobins have revealed that cooperativity exists between the alpha and the beta hemes of each dimeric half-molecule and have led to a symmetry rule for quaternary T-->R switching: the quaternary R structure is energetically favored over the T structure when each dimeric half-molecule contains at least one ligated subunit.