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Allosteric regulation of an enzyme. In the fields of biochemistry and pharmacology an allosteric regulator (or allosteric modulator) is a substance that binds to a site on an enzyme or receptor distinct from the active site, resulting in a conformational change that alters the protein's activity, either enhancing or inhibiting its function.
Allosteric regulations are a natural example of control loops, such as feedback from downstream products or feedforward from upstream substrates. Long-range allostery is especially important in cell signaling. [3] Allosteric regulation is also particularly important in the cell's ability to adjust enzyme activity.
The site that an allosteric modulator binds to (i.e., an allosteric site) is not the same one to which an endogenous agonist of the receptor would bind (i.e., an orthosteric site). Modulators and agonists can both be called receptor ligands. [2] Allosteric modulators can be 1 of 3 types either: positive, negative or neutral.
The particular arrangement of catalytic and regulatory subunits in this enzyme affords the complex with strongly allosteric behaviour with respect to its substrates. [3] The enzyme is an archetypal example of allosteric modulation of fine control of metabolic enzyme reactions. ATCase does not follow Michaelis–Menten kinetics.
These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism. In some cases, when a substrate binds to one catalytic subunit of an enzyme, this can trigger an increase in the substrate affinity as well as catalytic activity in the enzyme's other subunits, and thus the substrate acts as an activator.
Phosphofructokinase-1 (PFK-1) is one of the most important regulatory enzymes (EC 2.7.1.11) of glycolysis.It is an allosteric enzyme made of 4 subunits and controlled by many activators and inhibitors.
The cell is able to react to this kind of situation in a mechanical way and solve the problem of the amount of a product. An example of feedback inhibition in human cells is the protein aconitase (an enzyme that catalyses the isomeration of citrate to isocitrate). When the cell needs iron, this enzyme loses the iron molecule and its form changes.
Some activators have an allosteric site and can only function when a certain molecule binds to this site, essentially turning the activator on. [4] Post-translational modifications to activators can also regulate activity, increasing or decreasing activity depending on the type of modification and activator being modified.