  Hemoglobin exhibits allosteric structural changes upon ligand binding due to
the dynamic interactions between the ligand binding sites, the amino acids
residues and some other solutes present under physiological conditions. In the
present study, the dynamical and quaternary structural changes occurring in two
unligated (deoxy-) T structures, and two fully ligated (oxy-) R, R2 structures
of adult human hemoglobin were investigated with molecular dynamics. It is
shown that, in the sub-microsecond time scale, there is no marked difference in
the global dynamics of the amino acids residues in both the oxy- and the deoxy-
forms of the individual structures. In addition, the R, R2 are relatively
stable and do not present quaternary conformational changes within the time
scale of our simulations while the T structure is dynamically more flexible and
exhibited the T\rightarrow R quaternary conformational transition, which is
propagated by the relative rotation of the residues at the {\alpha}1{\beta}2
and {\alpha}2{\beta}1 interface.
