Hemoglobin relaxed structure

Reactivity. Hemoglobin can exist in either of two structural conformations, corresponding to the oxy (R, relaxed) or deoxy (T, tense) states. The key differences between these two structures are that the constrained T state has a much lower oxygen affinity than the R state and the T state has a lower tendency to dissociate into subunits that can be filtered in the kidneys. Therefore, stabilization of the T conformation would be expected to solve both the oxygen affinity and renal excretion problems. 

The quaternary structure observed m the deoxy form of hemoglobin is often referred to as the T (for tense) state because it is quite constrained by subunit—subunit interactions. The quaternary structure of the fully oxygenated form is referred to as the R (for relaxed) state. In light of the observation that the R form of hemoglobin is less constrained, the tense and relaxed designations seem particularly apt. Importantly, in the R state, the... 

We have deliberately not commented on the Isthmus yet. Here in the d-block, with electronic structures like [Ar]4s23d5 (that of manganese), the energy of chemical reactions is sufficient to remove the two s-electrons and a variable number of d-electrons. As a result, all manner of different types of cation can be formed. A major beneficiary of these relaxed circumstances are the processes of life, and also the technological superstructure that life erects from the soils of the kingdom. For example, iron appears as four bloody eyes in the center of the hemoglobin molecule, and its readiness to switch its complement... 

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