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Competitive Inhibition

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What is Competitive Inhibition?

MVSAT Dec 2023

The inhibition that is caused due to the impact of drugs and enzymes can be irreversible or reversible in nature. In the case of reversible inhibition, a state of equilibrium is easily established between the inhibitory drug and the enzyme. The irreversible inhibitions can be grouped into three types and these are known as competitive inhibition, uncompetitive inhibition, and non-competitive inhibition. 

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In the case of competitive inhibition, the drug will act as the mimic of the normal substrate and will compete against the actual substrate for the activated enzyme site. It is important for the concentration effects to exist in the case of competitive inhibition. In this article, students will learn more about competitive inhibition and see the competitive inhibition example. 

What are Reversible Inhibitors?

A reversible inhibitor results in the inactivation of a particular enzyme through certain noncovalent and reversed interactions. Unlike the irreversible inhibitors, the reversible ones can easily dissociate from the enzymes. Noncompetitive inhibition and competitive inhibition of enzymes are common examples of reversible inhibition. There is a third kind which is known as uncompetitive inhibition. 

Competitive Inhibition Definition and Process 

One of the easiest types of inhibition in enzymes would be competitive inhibition. It is the one that is most commonly used in the pharmaceutical industry. There are certain molecules that tend to act as competitive inhibitors of the enzyme. These molecules basically resemble the normal substrates that take place in the enzyme. A main competitive inhibition example can be seen in the case of methotrexate. This inhibitor resembles the appearance of the folate substrate that is present in the enzyme dihydrofolate reductase or DHFR. This is the enzyme responsible for the catalyzing action seen in the reduction reaction of folate which results in the creation of nucleotides.

With the presence of methotrexate, some particles of the enzyme will bind themselves to the methotrexate instead of binding to the folate that is present in the enzyme. Hence, for the time period during which the methotrexate is bound, the enzyme will remain inactive and hence will not be able to bind with the folate. Hence, the enzyme remains in an inhibited stage. It is important to note that the binding site of DHFR with the methotrexate is the active binding site. This is the same place where the binding with the folate should take place. Hence, the methotrexate parties compete with the folate for the enzyme binding process. With more quantities of methotrexate, the folate doesn’t have an active role to play in the enzyme. 

Non-Competitive Inhibition Definition and Process

In order to understand the difference between competitive and noncompetitive inhibition, one needs to know what the latter is in the first place. In this type of enzyme inhibition, the inhibitors that don’t have a resemblance with the substrate are involved in the process. One important thing in this type of inhibition is that the binding doesn’t necessarily occur in the active site. There is a separate site present in the enzyme where the binding occurs. The effect that is produced due to the binding of a non-competitive inhibitor to the enzyme is pretty different when compared to the competitive inhibitor. This difference occurs since there is no competition for the binding. 

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In the case of competitive inhibition, it is possible to reduce the effect of the inhibitor by increasing the amount of substrate in the enzyme. However, in the case of non-competitive inhibition, such inclusion will not make a difference. This means that even if the amount of the substrate in the enzyme is increased, there will be no effect on the percentage of the active enzyme. Hence, the percentage remains the same in all ranges.

Noncompetitive inhibition actually causes the reduction of the enzyme amount with the fixed amount of substrate concentration. One of the most common examples of such a type of inhibition is seen in feedback inhibition. This is one of the common biochemical processes that tend to use non-competitive inhibitors in order to control the enzymatic activity. This process is extremely useful in the synthesis of different amino acids.

By studying the enzyme inhibition, students can learn more about the different types of inhibition processes. In the case of competitive inhibition, the inhibitor and the substrate will compete for the binding site. In the case of non-competitive inhibition, the inhibitor as well as the substrate bind in different binding sites. In the case of uncompetitive inhibition, the inhibitor will bind to the enzyme-substrate complex.

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FAQs on Competitive Inhibition

1. When does competitive inhibition take place?

The case of competitive inhibition occurs when the inhibitor, as well as the substrate, tend to compete with each other in order to bind with the active site present in the enzyme. In order to make sure that the enzyme is working in a proper manner, it is important to fix the concentration ratio of the inhibitor or the substrate to the enzyme that is present in the process. Hence, it can be said that if the quantity of the inhibitor is increased, the substrate will have no effect on the binding process. In the case of competitive inhibition, when the substrate quantity is increased, the effect of the inhibitor on the enzyme will be reduced significantly.

2. How is competitive inhibition different from noncompetitive inhibition?

When it comes to the difference between both the processes, the most important thing to keep in mind is the role of the inhibitor. While it is seen that in the case of competitive inhibition, the substrate, as well as the inhibitor mimicking the substrate, will compete in order to bind properly to the enzyme, the case is entirely different in noncompetitive inhibition. One important feature of noncompetitive inhibition is that the substrate, as well as the inhibitor, will choose different sites in order to bind with the enzyme. So, while it is seen that increasing the amount of substrate will reduce the effect of the inhibitors in the case of competitive inhibition of enzymes, the same action doesn’t have an effect in the case of non-competitive inhibition.

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