Protein complexes are often referred to as oligomeric proteins. Oligomeric proteins are composed of subunits, with the subunits being individual polypeptide chains. Protein complexes have defined quaternary structural symmetries, if they are homo-oligomeric protein complexes where all subunits are identical. The quaternary symmetry are pseudo-symmetries if the complex is a hetero-oligomer. Homo- and hetero-oligomeric compositions allow for an additional regulatory hierarchy at the cellular, tissue, or organism level, where different combinations of subunits of heteromeric complexes, due to cell specific gene expression, often show minute, yet important differences in enzyme activity.
Hemoglobin, a tetrameric protein complex with
stoichiometry, belongs to globin protein family. The four binding sites in hemoglobin show positive cooperative binding, meaning that after the first binding site is occupied by an O2 molecule, the 3 remaining sites exhibit a largely increased affinity for O2 molecules. (Allostery and Cooperativity Hemoglobin. Text available at http://whatislife.com/reader/enzyme/enzyme.html ). Authorized alternative source: Peter Friedrich: Supramolecular enzyme organization. Quaternary structure and beyond. Pergamon Press, Oxford and Akademiai Kiado, Budapest 1984
The presented below modeling schema includes 3 approaches:
1. Hill model of cooperation
2. The MWC model of allosterism
3. Sequential KNF Model
