Allosteric Inhibition Definition
Allosteric inhibition is the slowing down of enzyme-catalyzed chemical reactions that take place in cells. These metabolic processes are responsible for the proper functioning and maintenance of balance in our body, and allosteric inhibition can help regulate these processes.
Essentially, metabolic processes break down and important molecules are formed. They are essential for everything from digesting the food we eat to repairing our muscles after exercise.
What is Allosteric Inhibition?
It has sometimes been found that when a series of reactions are catalyzed by a series of enzymes in sequence, the accumulation of the final product can cause an inhibition of the activity of the first enzyme in the series. This inhibition due to a compound (end product) that is completely different in structure from the enzyme’s substrate is called allosteric inhibition or feedback inhibition, and such an enzyme is called an allosteric enzyme.
This type of inhibition occurs due to the presence of an allosteric center (Greek allo = “other”; stereo = “space” or “place”) on the surface of the allosteric enzyme away from the active center. The final product molecule fits into the allosteric center and somehow changes the shape of the enzyme so that the active center of the enzyme becomes unsuitable for complexing with its substrate. Allosteric inhibition is reversible. When the concentration of the end product in the cell falls, it leaves the allosteric site and the activity of the allosteric enzyme is restored.
Lock and Key: Substrate Binds to Enzyme at the Active Site
Metabolic processes consist of a series of chemical reactions that produce end products. The most important drivers of metabolic processes are enzymes. Enzymes are specific proteins that catalyze reactions. These enzymes speed up important chemical reactions in cells by reducing energy requirements.
First, an enzyme binds to a substrate. This reaction then creates a product. The product can then serve as a subsequent substrate for another enzyme in the next metabolic step. After all, there is a chain of reactions that takes place until a final product is created.
An important point is that the binding of an enzyme and its substrate is very specific. The enzyme can be compared to a lock and the substrate to a key. Certain substrates can only bind to certain enzymes. They bind to a point on the enzyme called the “active site.”
Allosteric Inhibition Inhibits Enzymatic Activity
To control the rate of metabolic reactions, we have what is known as allosteric inhibition. Allosteric inhibitors slow enzyme activity by inactivating the enzyme. An allosteric inhibitor is a molecule that binds to the enzyme at an allosteric site. This site is not in the same location as the active site. When it binds to the inhibitor, the enzyme changes its three-dimensional shape.
Allosteric inhibition is a form of non-competitive inhibition. This means that the inhibitor at the active site does not compete directly with the substrate. Instead, it indirectly changes the composition of the enzyme.
After the shape change, the enzyme becomes inactive. It can no longer be bonded with its corresponding substrate. This then slows down the formation of by-products. Think of the allosteric inhibitor as a locksmith. The locksmith (that is, the allosteric inhibitor) changes the lock (that is, the enzyme) so that the key (that is, the substrate) can no longer open the lock (that is, the enzyme).
Allosteric Inhibition Prevents the Over-Accumulation of Products
Allosteric inhibitors prevent the body from wasting energy on unnecessary products. Think of a metabolic pathway like an assembly line in a factory. At each station on the assembly line, a machine changes the product before moving it to the next station. The assembly line then moves the intermediate products from one station to another until the final product is finished.
Let’s say this factory is in charge of making pants. In the first station, a machine cuts pants from raw material. Then a machine sews the hems of the pants together at the second station. In the third station, a machine places the zippers. Then a machine applies labels to the fourth station and places the product in the dispatch stack. When the machines are working properly, the assembly line runs smoothly and there are no jams. The stations produce products at similar prices.
However, imagine that one day the machine that attaches the zippers to the third station breaks down. There is a stop now. To prevent products from accumulating, we have to take the first stations on the supply line out of service. This is done to control the supply and demand of each intermediate product and to ensure that they are the same in each season.
Allosteric inhibition also slows down the chain of reactions. This will prevent excessive accumulation of unnecessary products.
Examples of Allosteric Inhibition
An example of an allosteric inhibitor is ATP in cellular respiration. This metabolic process works as a feedback loop. In this cycle, downstream products control the speed of the upstream reactions.
One enzyme involved in glycolysis is phosphofructokinase. It converts ADP to ATP. When there is too much ATP in the system, the ATP acts as an allosteric inhibitor. It binds to phosphofructokinase to slow down the conversion of ADP. In this way, ATP prevents unnecessary self-production. There is no need to produce more ATP when sufficient quantities are already available.
Allosteric Inhibition Definition