Allosteric proteins common features

Although haemoglobin is not a catalytic protein, it shares important features in common with enzymes, for example ligand binding, allosterism and inhibition . Before continuing, the reader should ensure familiarity with the concepts of allosterism as described in Section 3.2. 

A large number of enzymes exist as symmetric macro-molecular assemblies where they commonly exhibit C and D point group symmetries and contain two-, three-, four-, and six-fold axes of symmetry. In the simplest cases this feature provides additional thermodynamic stability for a protein that would otherwise be rather small. In more complex arrangements the protein-protein interfaces form the active site such that the oligomerization is required for function. Finally, in the most highly evolved enzymes there is communication between the active sites that reside on symmetrically related subunits. This provides the foundation for enzyme regulation as observed in most allosteric enzymes. 

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