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. Author manuscript; available in PMC: 2023 Apr 1.
Published in final edited form as: Mol Aspects Med. 2021 Jul 14;84:100971. doi: 10.1016/j.mam.2021.100971

Fig. 3.

Fig. 3.

The MWC two-state allosteric model. (Upper panel, quaternary structures) The main difference between the 2 quaternary structures is rotation of the symmetrically related αβ dimers of about 15 degrees. (Middle panel, model) Empty symbols designate deoxygenated subunits and filled symbols oxygenated subunits. KT (~0.001 torr−1) and KR (~1 torr−1) are the association constants for binding to the T and R quaternary structures, respectively, L (~5×105) is the ratio of the T to R population at zero oxygen pressure, and c = KT/KR. The approximate magnitude of the equilibrium constants is indicated schematically by the relative length of the arrows for the forward and backward reaction rates. (Lower panel, binding curves) The oxygen binding curve for both the R and T conformations is non-cooperative. The shift from the T to R conformation as successive molecules of oxygen bind results in the observed (obs) sigmoid shape, signifying cooperativity.