The quaternary structure of carbonmonoxy hemoglobin ypsilanti.

We present a geometric analysis of the allosteric interface in the new Y state quaternary structure observed in liganded mutant hemoglobin Ypsilanti (beta 99 Asp-->Tyr) by Smith, F.R., Lattman, E.E., Carter, C.W., Jr. (Proteins 10:81-91, 1991). The classical T to R quaternary structure change being a rotation of alpha beta dimers about an axis which is approximately parallel to the dimer axis of pseudosymmetry, the new quaternary structure is obtained by applying to R an additional rotation about an axis orthogonal to the first. This suggests that Y is a modified R state rather than an intermediate on the T to R pathway. Computer docking experiments designed to simulate the quaternary structure change support this suggestion.