Reversible Inhibition: Videos & Practice Problems

Reversible inhibition involves enzyme inhibitors that bind temporarily through non-covalent interactions, slowing down enzyme activity without completely halting it. This contrasts with irreversible inhibitors, which covalently bind and fully inactivate enzymes. Reversible inhibitors include competitive, uncompetitive, mixed, and non-competitive types, forming complexes that can dissociate, allowing normal enzymatic reactions to resume. Understanding these distinctions is crucial for grasping enzyme kinetics and regulation in biochemical pathways.

Reversible Inhibition

Alright. So now that we've covered irreversible inhibition, in this video we're going to introduce the opposite type of inhibition, reversible inhibition. Now, of course, reversible inhibition is going to be caused by reversible inhibitors, and reversible inhibitors are just enzyme inhibitors that, unlike irreversible inhibitors, will actually bind loosely, temporarily, and therefore, reversibly to an enzyme.

Now, recall from our previous lesson videos that irreversible inhibitors would completely stop or halt the enzyme's activity or initial reaction velocity, \( v_0 \). However, when it comes to reversible inhibitors, they don't stop or completely halt the enzyme's activity. Instead, what they do is they only just decrease or just slow down the enzyme's activity or initial reaction velocity. Also recall from our previous lesson videos that irreversible inhibitors used covalent bonds to bind to the enzyme, but with reversible inhibitors, they don't use covalent bonds; they use non-covalent interactions or non-covalent bonds to bind to the enzyme. And these non-covalent interactions are much weaker than the covalent interaction, so they're easier to break, and that's what allows these reversible inhibitors to bind to the enzyme reversibly.

Now, it turns out that reversible inhibitors include all of these different types of inhibitors that we're going to talk more about later in our course. These include competitive, uncompetitive, mixed, and non-competitive inhibitors. Down below, in our example of reversible inhibitors, notice that the reversible inhibitor, indicated by this 'I', is interacting with the free enzyme to form the enzyme-inhibitor complex, but some reversible inhibitors are also capable of interacting with the enzyme-substrate complex to form the ESI complex. But the most important thing about reversible inhibitors is that regardless of what type of inhibitor complexes form, whether it be the EI or the ESI complex, this complex forms reversibly and we can tell by these equilibrium arrows that are present here, which were not present when we covered irreversible inhibitors in our previous lesson videos.

And so this means that the inhibitor, after it forms a complex, is actually capable of breaking apart backwards and essentially allowing the reaction to proceed normally when it is not bound. So with reversible inhibitors, they only inhibit the reaction when they are bound, but as soon as they unbind, they do not inhibit the reaction.

Down below, you can see that we have all of the different types of reversible inhibitors that we're going to talk more about as we move forward in our course, which of course include competitive, uncompetitive, mixed, and non-competitive inhibitors. Now notice that we have mixed and non-competitive inhibitors grouped together here, and that's because it turns out that non-competitive inhibitors are really just a type of mixed inhibitor. And so we'll talk more about that later in our course, so I don't want you guys to worry about that right now. All I want you guys to know right now is that all of these inhibitors here are types of reversible inhibitors that we're going to talk more about later in our course.

So this concludes our introduction to reversible inhibition, and we'll be able to get more practice in applying these concepts later in our course. So I'll see you guys in our next video.

Reversible Inhibition

So now that we've covered both irreversible and reversible inhibitors, in this video we're going to directly compare them and briefly distinguish them from one another. Now when it comes to irreversible inhibitors, what's important to note is that irreversible inhibitors will completely inactivate the enzyme, and therefore it's going to completely stop or halt the enzyme's functional activity, which means which essentially translates to the initial reaction velocity equaling to 0 when the irreversible inhibitor is bound to the enzyme. Now, it's also important to note that irreversible inhibitors will interact with the enzyme covalently. So, it will be covalently bound and therefore it will be irreversibly bound. And so, that is indicated by this one-way reaction arrow for the formation of the complex, but it is not easily broken apart. Now that is in contrast to reversible inhibitors, which instead of completely inactivating the enzyme and stopping or halting the functional activity, they just slow down or decrease the enzyme's functional activity. So that just means that the initial reaction velocity will be decreased. And so, what's most important about reversible inhibitors is that they do not interact with the enzyme via covalent bonds. Instead, they interact via non-covalent interactions, which are very weak and it's very possible for the inhibitor to break apart reversibly and allow the enzymatic reaction to proceed normally, which is why it is, reversible inhibitors do not completely halt or stop the functional activity. And so, this allows us to directly compare and distinguish irreversible from reversible inhibitors. And again, as we move forward in our course, we're going to talk more and more about all of these different types of reversible inhibitors. So I will see you guys in our next lesson video.

Circle all of the true statements below:


a) Chymotrypsin catalyzes the hydrolysis of dietary carbohydrates.
b) The presence of an enzyme catalyst will affect the time taken for a reaction to reach equilibrium.
c) Reversible inhibitors are easier to purify from solutions of enzymes than irreversible inhibitors.
d) Irreversible inhibitors bind very tightly and sometimes covalently to enzymes.
e) The presence of an enzyme catalyst will alter the relative ratio of product to reactant for a biochemical reaction.

Alright. So this practice problem wants us to circle all of the true statements below. And looking at option a, it says that chymotrypsin catalyzes the hydrolysis of dietary carbohydrates. And we know from our previous lesson videos that this is definitely not true. We know that chymotrypsin is a peptidase and because it is a peptidase, it catalyzes the hydrolysis of peptide bonds in proteins and it does not catalyze the hydrolysis of dietary carbohydrates. So moving on to option b, it says that the presence of an enzyme catalyst will affect the time taken for a reaction to reach equilibrium. And, of course, we know that this is definitely true. Enzyme catalysts will speed up chemical reactions, so they're going to affect the time that it takes for a reaction to occur, and therefore it's going to speed up the reaction and allow the reaction to reach equilibrium at a faster rate in a shorter amount of time. And so because option b is a true statement, we'll go ahead and circle this option since it wants us to circle the correct answers. So, moving on to option c, it says that reversible inhibitors are easier to purify from the solutions of enzymes than irreversible inhibitors. And again, this is going to be a true statement, and we covered this in our last practice problem. And so the reason that option c is a true statement is that reversible inhibitors will bind reversibly to the enzyme, so it's a lot easier to purify the reversible inhibitors, whereas the irreversible inhibitors are going to be very difficult to purify because they will bind to the enzyme irreversibly, and so, when you try to purify the irreversible inhibitor by itself, it's going to be hard to do because it's going to be irreversibly bound to an enzyme as well. So moving on to option d, it says that irreversible inhibitors bind very, very tightly and sometimes covalently to enzymes. And again, we know that this is definitely true as well, so we can go ahead and circle it here. And that's because irreversible inhibitors, we know, can form covalent bonds to enzymes, but the most important thing is that they bind so tightly that, it ends up binding irreversibly to the enzyme. And so looking at our last option here, option e, it says that the presence of an enzyme catalyst will alter the relative ratio of product to reactant for a biochemical reaction. And so, the relative ratio of product to reactant is really defined by the equilibrium constant. And so we know that enzyme catalysts do not affect the equilibrium constant, and so we know that enzyme catalysts are not going to alter this ratio. And so, for that reason, we can go ahead and cross off option E because it's not true. And so the three correct answers for this practice problem are actually b, c, and d. And that concludes this practice, so I'll see you guys in our next video.

Here’s what students ask on this topic:

What is reversible inhibition in enzyme kinetics?

Reversible inhibition in enzyme kinetics refers to the temporary binding of inhibitors to enzymes through non-covalent interactions. Unlike irreversible inhibitors, which form covalent bonds and permanently inactivate enzymes, reversible inhibitors only slow down enzyme activity. This type of inhibition can be undone, allowing the enzyme to return to its normal function once the inhibitor dissociates. Reversible inhibitors include competitive, uncompetitive, mixed, and non-competitive types. These inhibitors form complexes with the enzyme or enzyme-substrate complex, which can dissociate, allowing the enzymatic reaction to proceed normally. Understanding reversible inhibition is crucial for studying enzyme regulation and biochemical pathways.

How do competitive and non-competitive inhibitors differ in reversible inhibition?

Competitive and non-competitive inhibitors are two types of reversible inhibitors that differ in their binding sites and effects on enzyme activity. Competitive inhibitors bind to the active site of the enzyme, directly competing with the substrate. This type of inhibition can be overcome by increasing substrate concentration. In contrast, non-competitive inhibitors bind to an allosteric site, not the active site, and do not compete with the substrate. This binding changes the enzyme's conformation, reducing its activity regardless of substrate concentration. Both types of inhibitors form reversible complexes, allowing normal enzyme function to resume once the inhibitor dissociates.

What are the main types of reversible inhibitors?

The main types of reversible inhibitors are competitive, uncompetitive, mixed, and non-competitive inhibitors. Competitive inhibitors bind to the enzyme's active site, competing with the substrate. Uncompetitive inhibitors bind only to the enzyme-substrate complex, preventing the reaction from proceeding. Mixed inhibitors can bind to both the free enzyme and the enzyme-substrate complex, affecting both substrate binding and catalysis. Non-competitive inhibitors, a subtype of mixed inhibitors, bind to an allosteric site, reducing enzyme activity without affecting substrate binding. All these inhibitors form reversible complexes, allowing the enzyme to return to its normal function once the inhibitor dissociates.

Why are non-covalent interactions important in reversible inhibition?

Non-covalent interactions are crucial in reversible inhibition because they allow the inhibitor to bind and dissociate from the enzyme easily. These interactions, which include hydrogen bonds, ionic bonds, and van der Waals forces, are much weaker than covalent bonds. This weak binding is essential for reversible inhibition, as it enables the inhibitor to temporarily reduce enzyme activity without permanently inactivating the enzyme. Once the inhibitor dissociates, the enzyme can return to its normal function, allowing the regulation of enzyme activity in response to cellular needs. Understanding these interactions is key to studying enzyme kinetics and regulation.

How does reversible inhibition affect enzyme activity?

Reversible inhibition affects enzyme activity by temporarily reducing the enzyme's ability to catalyze reactions. Unlike irreversible inhibitors, which permanently inactivate enzymes, reversible inhibitors bind through non-covalent interactions, allowing them to dissociate and enable the enzyme to regain its activity. Depending on the type of reversible inhibitor (competitive, uncompetitive, mixed, or non-competitive), the inhibition can affect substrate binding, enzyme-substrate complex formation, or the enzyme's catalytic efficiency. This temporary reduction in activity allows for fine-tuned regulation of metabolic pathways, ensuring that enzyme activity can be modulated in response to cellular conditions.