What is the composition of hemoglobin's quaternary structure?

Hemoglobin's quaternary structure is composed of a tetrameric arrangement, specifically consisting of two alpha (α) and two beta (ß) subunits, hence referred to as an α2ß2 tetramer. This arrangement is crucial for hemoglobin's function, allowing the protein to effectively transport oxygen throughout the body.

The tetrameric structure facilitates cooperative binding, meaning that the binding of oxygen to one subunit increases the affinity of the remaining subunits for oxygen. This behavior is essential for hemoglobin's functionality in oxygen delivery. The distinct arrangement of alpha and beta subunits also creates a specific interface that is important for the stability and functional regulation of hemoglobin.

In contrast to a monomer, dimer, or trimer, the tetrameric configuration of hemoglobin embodies the complex interactions necessary for its physiological role. The presence of both alpha and beta subunits allows hemoglobin to exist in different conformational states (tense and relaxed) as it binds and releases oxygen, which is not a feature of the simpler structural forms like monomers or dimers. Thus, the α2ß2 tetramer not only reflects hemoglobin's structural characteristics but is integral to its function as an oxygen carrier in the bloodstream.