Concerted model

Definition

The concerted model, also known as the Monod-Wyman-Changeux model, describes how allosteric enzymes exist in two distinct states: a relaxed (R) state that is active and a tense (T) state that is inactive. This model emphasizes that when one subunit of an enzyme transitions from the T state to the R state upon substrate binding, all other subunits of the enzyme simultaneously change to the R state. This cooperative behavior is critical in regulating enzyme activity and ensures a more efficient response to changes in substrate concentration.

5 Must Know Facts For Your Next Test

1. In the concerted model, all subunits of an allosteric enzyme exist in either the R or T state, and there is no mixture of states within the same enzyme complex.
2. The binding of a substrate stabilizes the R state, making it more favorable for other subunits to also adopt this active conformation.
3. This model explains why allosteric enzymes typically exhibit sigmoidal kinetics rather than Michaelis-Menten kinetics, reflecting their cooperative nature.
4. Allosteric inhibitors stabilize the T state, while activators promote the R state, thereby influencing enzyme activity and regulation.
5. The concerted model contrasts with the sequential model, which suggests that individual subunits can exist in different states during substrate binding.

Review Questions

• How does the concerted model explain the cooperative behavior seen in allosteric enzymes?
  • The concerted model explains cooperative behavior by stating that all subunits of an allosteric enzyme are either in the active R state or inactive T state. When one subunit binds to a substrate and transitions to the R state, all other subunits are compelled to follow suit and also adopt the R state. This concerted shift enhances the overall enzyme activity and allows for a more coordinated response to substrate concentration changes.
• Compare and contrast the concerted model with the sequential model in terms of enzyme behavior and cooperativity.
  • The concerted model posits that all subunits of an enzyme transition simultaneously between two states (R and T), emphasizing a more rigid form of cooperativity. In contrast, the sequential model allows for individual subunits to change conformation independently as substrates bind. This means that in the sequential model, it's possible for some subunits to be in different states at once. Consequently, while both models describe cooperativity, they differ fundamentally in how they portray interactions between subunits during substrate binding.
• Evaluate the implications of the concerted model for understanding metabolic regulation and drug design.
  • Understanding the concerted model has significant implications for metabolic regulation as it reveals how enzymes can be finely tuned through allosteric effects. This knowledge is crucial for drug design, as it helps scientists create molecules that can act as allosteric modulators—activating or inhibiting enzyme activity in specific pathways. By targeting allosteric sites rather than active sites, drugs can achieve desired effects with potentially fewer side effects, making it a valuable approach in therapeutic development.

Related terms

allosteric regulation: The process by which an enzyme's activity is modified through the binding of an effector molecule at a site other than the active site.

cooperativity: The interaction among subunits of an enzyme where the binding of a substrate to one subunit affects the binding affinity of other subunits.

sigmoidal kinetics: A type of enzyme kinetics characterized by a sigmoidal (S-shaped) curve, indicating that the rate of reaction is dependent on substrate concentration in a cooperative manner.