Please be detailed, but understandable. Thank you! :)
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An allosteric inhibitor decreases the ability for a substrate to reach an active site by stabilizing the inactive form of the enzyme.
Example:
An example of an allosteric inhibitor is strychnine, a convulsant poison, which acts as an allosteric inhibitor of glycine. Glycine is a major post-synaptic inhibitory neurotransmitter in the spinal cords and brain stems of mammals. Its binding lowers the affinity of the glycine receptor for glycine. Strychnine, thus, inhibits the action of an inhibitory transmitter, causing convulsions.
Phosphofructokinase (PFK) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose-6-phosphate:
fructose-6-phosphate + ATP fructose-1,6-bisphosphate + ADP
In part because of the irreversible nature of this step in glycolysis, PFK is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In this case, PFK's activity is inhibited by allosteric regulation by ATP itself, closing the valve on the flow of carbohydrates through glycolysis. Recall that allosteric regulators bind to a different site on the enzyme than the active (catalytic) site. Thus ATP binds in two places on PFK: in the active site as a substrate and in the regulatory site as a negative modulator. ATP bound in the regulatory site acts as a modulator by lowering the affinity of PFK for its other substrate, fructose-6-phosphate.
Example:
An example of an allosteric inhibitor is strychnine, a convulsant poison, which acts as an allosteric inhibitor of glycine. Glycine is a major post-synaptic inhibitory neurotransmitter in the spinal cords and brain stems of mammals. Its binding lowers the affinity of the glycine receptor for glycine. Strychnine, thus, inhibits the action of an inhibitory transmitter, causing convulsions.
Phosphofructokinase (PFK) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose-6-phosphate:
fructose-6-phosphate + ATP fructose-1,6-bisphosphate + ADP
In part because of the irreversible nature of this step in glycolysis, PFK is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In this case, PFK's activity is inhibited by allosteric regulation by ATP itself, closing the valve on the flow of carbohydrates through glycolysis. Recall that allosteric regulators bind to a different site on the enzyme than the active (catalytic) site. Thus ATP binds in two places on PFK: in the active site as a substrate and in the regulatory site as a negative modulator. ATP bound in the regulatory site acts as a modulator by lowering the affinity of PFK for its other substrate, fructose-6-phosphate.