Enzyme Inhibition: Study with Video Lessons, Practice Problems & Examples

Enzyme inhibition reduces reaction rates through small molecules or ions that bind to enzymes. In competitive inhibition, the inhibitor occupies the active site, blocking substrate access, while in noncompetitive inhibition, it binds elsewhere, altering the enzyme's shape. Reversible inhibition allows enzyme activity to be restored, whereas irreversible inhibition leads to permanent loss. Examples include ibuprofen for competitive inhibition and heavy metals for noncompetitive. Understanding these mechanisms is crucial for grasping enzyme functionality and metabolic pathways.

Enzyme Inhibition Concept 1

Now, when it comes to enzyme inhibition, we're going to say that inhibition itself decreases catalyzed reaction rates. And we're going to say that the inhibitor itself is a small molecule or ion that binds to the enzyme and interferes with its activity. Now the characteristics of inhibition, we can talk about it in terms of competitive versus noncompetitive and reversible versus irreversible. Now in competitive inhibition, we're going to say the inhibitor binds to the active site of the enzyme. It's going to block that active site from the substrate, so it can't come in. Noncompetitive inhibition means that the inhibitor binds to a non-active site, so like an allosteric site. And then we're going to say reversible. Well, reversible means that the enzyme can regain or enzyme regains its activity or can regain its activity. Irreversible means that we have a permanent loss of enzyme activity. So these are the different types of inhibitions that overall will hurt or decrease in enzymes' effectiveness and activity.

Enzyme Inhibition Concept 2

So in this video, we're going to take a look at the different types of inhibition: Competitive versus noncompetitive, reversible versus irreversible. So if we take a look at the first one, we're going to say we have reversible competitive inhibition. Here we have our substrate, and within the active site of our enzyme, we have the inhibitor in place. Now, here we're going to say that the inhibitor is similar in shape and size to the substrate. So it can take up the active site instead of the substrate. A great example of this is Ibuprofen. Now, what's the interaction here? Well, here this would be a non-covalent interaction between the inhibitor and the enzyme at the active site. And what is the effect? Well, the effect we can see is that it's taking up that active site position, so it's blocking it from the substrate. And how do we reverse this effect? How could we get that inhibitor to not get in the way of our substrate? Well, increasing the concentration of our substrate would help to lower the effect of this inhibitor.

Now, reversible noncompetitive. Here, we have our active site, we have our substrate, and then down here we have our inhibitor. It attached somewhere else that is not the active site. So here we're going to say that when it comes to the inhibitor, it does not resemble the substrate's shape because it's not binding to the active site where the substrate would go. A great example of this are heavy metals. Now here this is also non-covalent in terms of interaction, but now it's at the non-active site. Here, we're going to say it causes a shape change in the enzyme and in the active site. But by the enzyme, the inhibitor attaching itself to this part down here, which is not the active site, it's actually going to cause a shift or change in the shape of this active site. It changes shape so the substrate can no longer attach effectively to the enzyme. Here, we're going to say, how could we reverse this effect? Well, we have to use special types of agents. They would have to bind to the inhibitor so that they cannot bind to the non-active site and change the active site of the enzyme.

Finally, we have irreversible. Here we have our substrate, we have our enzyme, and the inhibitor has attached to the active site. Here we would say that when it comes to the inhibitor, it does not resemble the substrate's shape. In this case, we could talk about poisons and different types of venoms belonging to this type of inhibition. Now, here we're going to say we have a covalent interaction with our group within the active site. And we're going to say here that the effect is it blocks the active site. The inhibitor is attaching itself to that active site. And here the inhibition is permanent. So this can do some long-lasting damage and effects in terms of irreversible inhibition. So we've talked about the different types of inhibition, remember, competitive versus noncompetitive, reversible versus irreversible.

Enzyme Inhibition Example 1

Here in this example question, it says, match each type of inhibition with the correct statement. So a is reversible competitive, b is reversible noncompetitive, and c is irreversible. The first one says, inhibitor decreases enzyme activity by binding at a site other than the active site. Well, remember, in our different types of inhibition that we covered, we'd say that the reversible noncompetitive is the only one that has the inhibitor binding to a site that is not the active site. So first, it's going to be B. Next, the formation of strong covalent bond leads to permanent loss of enzyme activity. So, remember, when it comes to irreversible inhibition, it's the covalent of the R groups that are binding to the active site. Also, it says permanent. Remember, the effect here is permanent when it comes to irreversible. So this would be C. Next, the substrate is unable to bind with the active site due to a change in enzyme structure. Alright. So for this one, they're talking about the active site changing form. This happens when the inhibitor attaches to the nonactive site. It causes what we call a conformational change in our active site. The shape changes so the substrate can no longer effectively attach to it. This happens with reversible noncompetitive inhibition. Next, an increase in the concentration of substrate increases the reaction rate. We said that the reversible competitive inhibition, its effects can be reversed if we increase the amount of substrate. This is going to put the inhibitor at a disadvantage where it won't be able to effectively bind to the active site. So here, this would be A. So we'd say that the statements would be B, C, B, and A for this particular example question.

Which of the following inhibitors could be a reversible competitive inhibitor for acetylcholinesterase if its substrate is acetylcholine?

• A.
• B.
• C.

Here’s what students ask on this topic:

What is the difference between competitive and noncompetitive enzyme inhibition?

Competitive inhibition occurs when an inhibitor binds to the active site of an enzyme, preventing the substrate from binding. The inhibitor often resembles the substrate in shape and size. This type of inhibition can be overcome by increasing the concentration of the substrate. Noncompetitive inhibition, on the other hand, involves the inhibitor binding to a site other than the active site, known as an allosteric site. This binding changes the enzyme's shape, making the active site less effective or inaccessible to the substrate. Noncompetitive inhibition cannot be overcome by simply increasing substrate concentration.

How does reversible enzyme inhibition differ from irreversible enzyme inhibition?

Reversible enzyme inhibition is characterized by the temporary binding of an inhibitor to an enzyme, allowing the enzyme to regain its activity once the inhibitor is removed. This type of inhibition often involves non-covalent interactions. Irreversible enzyme inhibition, however, involves the permanent binding of an inhibitor to an enzyme, usually through covalent bonds. This leads to a permanent loss of enzyme activity. Examples of irreversible inhibitors include certain poisons and venoms.

Can you provide examples of competitive and noncompetitive inhibitors?

Yes, a common example of a competitive inhibitor is ibuprofen, which competes with the substrate for the active site of the enzyme. For noncompetitive inhibitors, heavy metals like lead and mercury are good examples. These metals bind to sites other than the active site, causing a change in the enzyme's shape and reducing its activity.

What are the effects of enzyme inhibition on metabolic pathways?

Enzyme inhibition can significantly impact metabolic pathways by reducing the rate of enzyme-catalyzed reactions. Competitive inhibition can be overcome by increasing substrate concentration, allowing the pathway to continue. Noncompetitive inhibition, however, alters the enzyme's shape, making it less effective regardless of substrate concentration. Irreversible inhibition can permanently shut down a pathway, leading to potential cellular damage or death. Understanding these effects is crucial for drug development and disease treatment.

How can the effects of reversible competitive inhibition be reversed?

The effects of reversible competitive inhibition can be reversed by increasing the concentration of the substrate. Since the inhibitor competes with the substrate for the active site, a higher substrate concentration increases the likelihood that the substrate will bind to the active site instead of the inhibitor. This effectively reduces the impact of the inhibitor on the enzyme's activity.