Hemoglobin tetrameric structure

In many cases there are important interactions between protein molecules that may lead to highly organized structures such as the pleated sheet of silk fibroin (Figure 25-13) or the coiling of a helices, as found in a-keratins, the fibrous proteins of hair, horn, and muscles (Figure 25-17). This sort of organization of protein molecules is called quaternary structure and is an important feature of many proteins that associate into dimers, tetramers, and so on. The tetrameric structure of hemoglobin is an important example. 

The other new region provided by the tetrameric structure of hemoglobin is the interface between unlike subunits, the a-b interface. At this interface, the two subunits are held together by a number of salt linkselectrostatic bondsand by hydrogen bonds. 

The Gd-DOTP chelate (Fig. 18) has been examined as a potential allosteric effector of hemoglobin [113]. Human hemoglobin is a tetrameric protein whose quaternary structure is affected by an allosteric effector. Binding of this low molecular weight species stabilizes the so-called T-form of hemoglobin, which is characterized by a low oxygen affinity, as opposed to the R-form, a very efficient... 

Hemoglobin (Hb) is a tetrameric protein composed of two identical alpha subunits and two identical beta subunits. X-ray crystal structures of the low (18) and high (20) affinity states of this protein have been solved at high resolution. 

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