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A substrate is turned into a product through its interaction with an enzyme. That product will often become the substrate for the next reaction in a metabolic cycle or pathway, which will require a different type of enzyme.
Have you ever hid your favorite junk food behind something else in the pantry, as a kind of “defense mechanism” against yourself? Or perhaps you’ve set limits for yourself, created a monthly spending budget, or organized a rigid schedule for how you spend your time. These tools are a means to control your behavior, either activating positive changes or inhibiting negative ones. This is an important form of conscious, active control on the macrocosmic scale.
As is so often found in nature, the microscopic scale similarly works on a regulatory system of activation and inhibition of specific enzymes; this collection of processes is known as allosteric regulation. Before we dig into the details of allosteric regulation, it is important to take a quick refresher on enzymes, namely their critical role in our body.
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Enzymes
At the most basic definition, enzymes are specialized proteins that initiate changes in the body. In the trillions of biochemical reactions happening in our cells every minute, enzymes play the key role of catalyzing those reactions. This is not to say that those reactions would not occur normally, but enzymes speed up the rate of those processes. Enzymes are reusable proteins that are tailored for a specific type of reaction within a series or cycle of reactions. A substrate is turned into a product through its interaction with an enzyme. That product will often become the substrate for the next reaction in a metabolic cycle or pathway, which will require a different type of enzyme.
The delicate interplay of enzymes and elaborate metabolic pathways is what sustains critical processes we need to survive, from the generation of usable energy to the replication of DNA. There are approximately 3,000 different enzymes found within the body, each serving a unique and valuable purpose to our cells, tissues and organs!
Also Read: Why Are Enzymes Important And How Do They Work?
Allosteric Regulation Definition
Enzymes are effective and reusable, and will continue certain chemical processes if there is additional substrate to work with. For that reason, some amount of regulation is required to ensure efficiency and prevent the waste of any excess resources. For example, imagine if you owned a bakery and one of your new employees used up all the flour, sugar and chocolate making muffins all day, but failed to make any cookies, cakes, pies or brownies. Some form of regulation or control must be in place to make sure that all of the important recipes (processes) are carried out. At the enzymatic, microscopic level, this control mechanism is called allosteric regulation.
Also Read: What Is Feedback Inhibition?
How Does Allosteric Regulation Work?
Now, for any enzymatic reaction to occur, the substrate must bond with the enzyme at an active site. These sites on an enzyme include a binding site and a catalytic site, which temporarily hold the substrate in place and facilitate the chemical reaction, respectively. Once the enzymatic reaction is completed, the product is released from the active site, leaving it open for another substrate to bind.
However, once enough enzymatic reactions of the same type occur, leading to the creation of as many products as necessary, the enzymes need to be regulated. The way that this is done is through the involvement of effector molecules, typically “small molecules”, which are classified based on their activity and molecular size. When these molecules bind to an allosteric site (regulatory site), rather than the active site of an enzyme, the protein changes its shape slightly. These effector molecules can function as activators or inhibitors, meaning that the change to the protein will increase the rate of the reaction, or prevent further binding of substrates at the active site, respectively. In short, an activator will increase the reaction rate, while an inhibitor will decrease the rate or stop it entirely.
“Turning off” an enzymatic reaction prevents the cell from wasting resources and energy, while “supercharging” an enzymatic reaction will help the cells/body with immediate metabolic demands. Allosteric activation increases the attraction of active sites and substrates, while allosteric inhibition decreases the attraction between binding sites and potential substrates.
These small effector molecules have a number of different potential roles in cells and throughout the body, and can also have an impact on cell signaling, gene expression and RNA transcription, among others. It is also important to note that such effector molecules can be either artificial or natural; our body uses the molecules available for allosteric control, when necessary, but humans have also figured out how to create functional allosteric regulation molecules. It may not come as a surprise to learn that many of these “small molecules” are actually pharmaceutical drugs! It makes sense that medication would be able to play such an important role in allosteric regulation. If a doctor wants to speed up or slow down a certain metabolic process in the body, perhaps to avoid further symptoms or correct a deficiency, allosteric regulation or modulation is an effective means to do so.
As mentioned at the beginning of this article, there are trillions of enzymatic reactions happening every minute of our lives, and those chemical processes have a major impact on health. Providing the body with small molecules (pharmaceuticals) that can alter or control those processes is a very important tool in the medical field.
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