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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 enzyme is an archetypal example of allosteric modulation of fine control of metabolic enzyme reactions. ATCase does not follow Michaelis–Menten kinetics. Instead, it lies between its low-activity, low-affinity "tense" and its high-activity, high-affinity "relaxed" states. [4]
This type of enzymes presents two binding sites: the substrate of the enzyme and the effectors. Effectors are small molecules which modulate the enzyme activity; they function through reversible, non-covalent binding of a regulatory metabolite in the allosteric site (which is not the active site).
Tissue-specific changes in PFK activity and isoenzymic content contribute significantly to the diversities of glycolytic and gluconeogenic rates which have been observed for different tissues. [4] PFK1 is an allosteric enzyme and has a structure similar to that of hemoglobin in so far as it is a dimer of a dimer. [5]
Many of these allosteric regulators act at the E1 domain of the enzyme complex, but all three domains of the enzyme complex can be allosterically controlled. [7] The activity of the enzyme complex is upregulated with high levels of ADP and Pi, Ca2+, and CoA-SH.
In addition, the enzyme transferase shifts a block of 3 glucosyl residues from the outer branch to the other end, and then a α1-6 glucosidase enzyme is required to break the remaining (single glucose) α1-6 residue that remains in the new linear chain. After all this is done, glycogen phosphorylase can continue.
The allosteric binding site in PC offers a target for modifiers of activity that may be useful in the treatment of obesity or type II diabetes, and the mechanistic insights gained from the complete structural description of RePC (R. etli) permit detailed investigations into the individual catalytic and regulatory sites of the enzyme. [17]