In biochemistry, a macromolecule has cooperative binding if when binding a ligand, the affinity of the ligand for the molecule changes depending on the amount of ligand already bound. A macromolecule is said to have positive cooperativity if the binding of ligand increases affinity for the ligand, and negative cooperativity if the affinity for the ligand decreases as more ligand is bound. A macromolecule is noncooperative if the amount of ligand bound does not affect the binding affinity at all. (In this last case, the way the affinity depends on the concentration of ligand in solution often is described as "hyperbolic," because a graph of this dependence traces a hyperbola). In case of positive cooperativity, the resulting graph is often described as "sigmoid," after its subtle "S"-shape. The degree of cooperativity is quantified by use of the Hill Coefficient. Biochemistry is the chemistry of life, a bridge between biology and chemistry that studies how complex chemical reactions give rise to life. ... A macromolecule is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. ... In chemistry, a ligand is an atom, ion or functional group that is bonded to one or more central atoms or ions, usually metals generally through coordinate covalent bond. ... Concentration is a very common concept used in chemistry and related fields. ... A graph of a hyperbola, where h = k = 0 and a = b = 2. ... In biochemistry, the binding of a ligand to a macromolecule is often enhanced if there are already other ligands present on the same macromolecule (this is known as Cooperative binding). ...

See also: quaternary structure -- enzyme allostery In biochemistry, many proteins are actually assemblies of more than one protein (polypeptide) molecule, which in the context of the larger assemblage are known as protein subunits. ... In biochemistry, an enzyme or other protein is allosteric if its activity or efficiency changes in response to the binding of an effector molecule at a so-called allosteric site. ...