Navigation Links

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. Changes that enhance activity are referred to as allosteric activation, while the opposite is called allosteric inhibition. "Allostery" is derived from the Greek "other site", referring to the typical scenario in which an enzyme's allosteric and active sites are distinct.


Models of allostery

Most allosteric effects can be explained by either the concerted (MWC) model put forth by Monod, Wyman, and Changeux, or by the sequential model described by Koshland, Nemethy, and Filmer. Both postulate that enzyme subunits exist in one of two conformations, tensed (T) or relaxed (R), and that relaxed subunits bind substrate more readily than those in the tense state. The two models differ most in their assumptions about subunit interaction.

Concerted model

The concerted model of allostery postulates that enzyme subunits are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits. Thus all subunits must exist in the same conformation. The model further holds that in the absence of any ligand (substrate or otherwise), the equilibrium favors the T state over the R state. To summarize:

  • all subunits must exist in the same conformation
  • equilibrium favors the T state over the R state

The binding of substrate to one subunit causes all other subunits to assume the R state, thereby enhancing their affinity for substrate.

Sequential model

The sequential model of allostery holds that subunits are not connected in such a way that a conformational change in one induces a similar change in the others. Thus all enzyme subunits need not exist in the same conformation. Moreover, the sequential model dictates that molecules of substrate bind via an induced fit protocol. Namely, when a subunit randomly collides with a molecule of substrate, the active site essentially forms a glove around its substrate. While such an induced fit converts a subunit from the tensed to relaxed state, it does not propagate the conformational change to adjacent subunits. Instead, substrate binding at one subunit only slightly alters the structure of other subunits so that their binding sites are more receptive to substrate. To summarize:

  • subunits need not exist in the same conformation
  • molecules of substrate bind via induced fit protocol
  • conformational changes are not propagated to all subunits
  • substrate binding causes increased substrate affinity in adjacent subunits

Allosteric activation

Allosteric activation, such as the binding of oxygen molecules to haemoglobin, occurs when the binding of one ligand enhances the attraction between substrate molecules and other binding sites. With respect to hemoglobin, oxygen is effectively both the substrate and the effector. The allosteric, or "other," site is the active site of an adjoining protein subunit. The binding of oxygen to one subunit induces a conformational change in that subunit that interacts with the remaining active sites to enhance their oxygen affinity.

Allosteric inhibition

Allosteric inhibition occurs when the binding of one ligand decreases the affinity for substrate at other active sites. For example, when 2,3-BPG binds to a regulatory site on hemoglobin, the affinity for oxygen of all subunits decreases or increases.

Related topics


(Date:10/29/2014)... their food, but they also need protection from its harmful ... of molecules in plants that shields them from sun damage. ... American Chemical Society , one team reports on the mechanics ... and colleagues at Purdue University note that the harsh ultraviolet ... to plant DNA and, as a result, hinder plant growth. ...
(Date:10/29/2014)... their types and numbers of bugs and bacteria ... the difference between a closed case and an ... a more than $866,000 U.S. Department of Justice ... changing populations. The microbial communities may provide crucial ... race, socioeconomic relations and more, said Eric Benbow, ...
(Date:10/29/2014)... MA and Hebei, China — BGI Tech and Hebei ... of the Jujube genome. Jujube is the most economically ... genome is particularly difficult to sequence due the high ... the first time that a genome in the Rhamnaceae ... recently published in Nature Communications . ...
Breaking Biology News(10 mins):MSU partners with Detroit to investigate death scenes 2BGI Tech and Hebei Agricultural University complete the genome sequencing of the jujube tree 2
... OAK RIDGE, Tenn. -- A tree outside Oak ... the inspiration for a discovery that may ultimately lead ... and more. Just as a breeze causes leaves, ... at the molecular level perform hundreds of chemical processes ...
... -- The Techna Institute, an innovation hub poised to ... new healthcare technologies, launches today at University Health Network ... Dr. Christopher Paige, VP, Research at UHN ... research and development. Technological innovation holds the key to ...
... MEDFORD/SOMERVILLE, Mass. A new approach to studying ... assistant professor of biomedical engineering in Tufts University,s,School of ... March of Dimes Foundation. Kuo,s research could yield ... that occur in utero, such as clubfoot, which requires ...
Cached Biology News:ORNL fundamental discovery casts enzymes in new light 2UHN, University of Toronto launch Techna innovation hub to get health technologies to patients faster 2Tufts University researcher develops living tissue 2
Other biology definitionOther Tags