Structural Biochemistry/Protein function/Binding Sites/Cooperativity/Allosterism

Allosterism a characteristic of certain enzymes. These particular enzymes can have its effectiveness altered by the enzyme changing its tertiary structure. This change in tertiary structure alters the reactivity of other binding sites, possibly increasing substrate affinity at these other sites. As a result, the binding can become cooperative, which means that binding at one site can increase the chances of a substrate binding to other sites. This leads to sigmoidal graphs of substrate concentration versus reaction velocity. On a side note, these allosteric enzymes do not obey Michaelis-Menten Kinetics. They do not obey the Michaelis-Menten Kinetics because the rate of product v.s substrate concentration resembles a "S" curve and a sigmoidal kinetics. And that sigmoidal kinetics result from cooperativity, which is the binding of substrate to an active site will facilitate the binding of other substrates to other active sites.

An example of Allosterism is the Allosteric effectors of Carbon Dioxide and Hydrogen ions in red blood cells. The Allosteric Hemoglobin has hydrogen ions and Carbon dioxide that will bind to other sites on hemoglobin that will alter the actual active sites of the hemoglobin. In this case, the hydrogen ion and Carbon dioxide will bind to hemoglobin that will result in the decrease of the affinity of hemoglobin for oxygen.