What is an Allosteric Site?
- Enzymes have a primary active site where substrates bind.
- However, many enzymes also have a secondary site, the allosteric site, located elsewhere on the enzyme.
- Only certain molecules, called allosteric effectors, can bind to these sites. These molecules are often products or intermediates of metabolic pathways.
- The binding of molecules to the allosteric site is reversible, once the molecule dissociates, the enzyme returns to its original state.
Definition
Allosteric site
A site on an enzyme other than the active site, where specific molecules can bind to regulate enzyme activity.
- Think of an enzyme as a flexible tool.
- Binding at the allosteric site is like adjusting a screw on the tool, changing its shape and function.
How Allosteric Regulation Works
- When an allosteric regulator binds to the allosteric site, it causes a conformational change in the enzyme’s structure.
- This change affects the enzyme’s active site, either enhancing or inhibiting its ability to catalyze a reaction.
Allosteric activation and inhibition
- Allosteric Activation: When an activator molecule binds to the allosteric site, it can cause the active site to adopt a shape that increases its affinity for the substrate, thus enhancing enzyme activity.
- Allosteric Inhibition: When an inhibitor molecule binds to the allosteric site, it induces a conformational change that prevents the substrate from binding to the active site, thereby reducing or halting enzyme activity.
Non-Competitive Inhibition: A Closer Look
- In non-competitive inhibition, the inhibitor binds to an allosteric site, distinct from the active site, but instead of blocking substrate binding, it alters the enzyme’s shape so that the active site is no longer functional for catalysis.
- This means they can inhibit the enzyme regardless of how much substrate is present.
