Degree of Inhibition - Video Tutorials & Practice Problems
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Degree of Inhibition
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Alright. So now that we've introduced the inhibition constant, the next topic that we're going to cover before we actually get into the details of the different types of reversible inhibitors is the degree of inhibition. So recall from our previous lesson videos, we said that enzyme inhibitors by definition will decrease the initial reaction rate or velocity v naught of an enzyme catalyzed reaction. But here we have a question and really it's just asking how can biochemists measure the inhibitor effects on the initial reaction velocity v naught of an enzyme catalyzed reaction? And it turns out that the answer to this question is the degree of inhibition. And so the degree of inhibition is really just a factor that measures and quantifies how much an enzyme is being inhibited by the inhibitor. And so recall from our previous lesson videos that enzyme inhibitors can either bind to the free enzyme to form the e I complex or enzyme inhibitors could also bind to the enzyme substrate complex to form the e s I complex, and because enzyme inhibitors can bind to either the free enzyme or the enzyme substrate complex, biochemists can actually separately measure the degree of inhibition on the free enzyme and the enzyme substrate complex. And so in our next lesson video, we're going to focus on the degree of inhibition on the free enzyme, but later in a separate video, we'll talk about the degree of inhibition on the enzyme substrate complex. And so I'll see you guys in our next video.
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concept
Degree of Inhibition
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Alright. So in this video, we're going to talk about the degree of inhibition on the free enzyme. And so the degree of inhibition on the free enzyme is represented with the Greek variable alpha. And so the degree of inhibition on the free enzyme alpha is just equal to 1 plus the ratio of the concentration of inhibitor over the inhibition constant that we talked about in our previous lesson videos. And so this degree of inhibition on the free enzyme alpha is a unitless factor that is always greater than or equal to 1. And so here you can see that alpha will always be greater than or equal to 1. Now when there's no inhibitor present at all, that means that alpha is going to equal exactly 1. And then as alpha begins to increase, then the concentration of inhibitor will also increase. So a value of alpha greater than 1 means that there is inhibitor present. And, of course, the greater alpha is, the more inhibitor is present. And so if we take a look at our image down below, notice over here on the left hand side what we have is the same enzyme catalyzed reaction that we've seen so many times before in our previous lesson videos. And so here in this video, we're specifically focusing on, again, the degree of inhibition on the free enzyme alpha. And so that means that the inhibitor here is gonna be only inhibiting the free enzyme as we see here. And so, of course, we know that when the inhibitor is bound to the enzyme, no reaction is able to take place. And so, here what we can see, again, what we're emphasizing is that the degree of inhibition on the free enzyme is equal to the variable alpha. And alpha is just equal to, again, one plus this ratio here of the concentration of inhibitor over the inhibition constant. And so, if we take a second and think about what this here actually means, we know that, of course, the concentration of inhibitor is either gonna be 0 or some positive number. We're never gonna have a negative number for the concentration of inhibitor. And we know from our previous lesson videos that the inhibition constant KI also represents a specific concentration of inhibitor. It's the exact concentration of inhibitor that allows for half of max maximum inhibition. And so, if we have 2 concentrations here that are both positive, then that means that this ratio here is going to be positive. And of course, any positive number here, plus 1, is going to be greater than 1. And in this equation right here, there's no way that alpha is going to be less than 1. And so here, in our chart below where it says alpha is less than 1, what we can write is that it's simply not possible to have an alpha less than 1. And we're never we're never gonna see that, in our, course. And so also notice that, if alpha is exactly equal to 1, as we mentioned up above in our lesson, if alpha is equal to 1, that means that there's going to be no inhibitor present. So essentially the inhibitor is going to be absent Or we could just say that there's no inhibitor present when alpha is equal to 1. Now in our last scenario here we can see if alpha is greater than 1, that means that the inhibitor is indeed present and it will be inhibiting the enzyme. And so, we'll be able to get some, I'll be able to show you guys an example of how to utilize this degree of inhibition on the free enzyme alpha, in our next video. So I will see you guys there.
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example
Degree of Inhibition Example 1
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Alright. So, here we have an example problem that's asking according to the data in the table below shown right here, which enzyme is affected most by the inhibitor? Is it enzyme A, enzyme B, or enzyme C? And so taking a look at this table over here, notice that for each of these three enzymes, we're given the degree of inhibition that the inhibitor has on each enzyme. And so of course, the enzyme that has the greatest degree of inhibition is gonna be the one that's going to be inhibited the most. And so enzyme b, because it has the greatest degree of inhibition here, it's going to be the one that's inhibited the most. And so we can go ahead and say that it's enzyme b here that is, the correct answer for this example. Now, of course, we know that if the degree of inhibition is equal to 1, then what that means is, alpha will be equal to 1. And, if this is the case, that means that there will be essentially no inhibitor present, essentially as if the inhibitor were absent. And so, notice here that enzyme c has an alpha that is, really close to equaling to 1. It's 1.02. And so what this means is that really the inhibitor has a very, very small, small small effect on enzyme C and it doesn't really inhibit enzyme C that much. And so the main takeaway here that we wanna get is that the greater the degree of inhibition, the more that enzyme will be inhibited by that enzyme inhibitor. And so, this here concludes our example, and I'll see you guys in our next video where we'll be able to get some practice.
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Problem
Problem
Calculate the degree of inhibition of an inhibitor on the free enzyme if the [I] = 3 μM and the KI = 6 μM.
A
α = 1.5
B
α = 2
C
α = 4
D
α = 3.5
E
α = 0.5
5
concept
Degree of Inhibition
Video duration:
2m
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Video transcript
Alright. So now that we've covered the degree of inhibition on the free enzyme, in this video we're going specifically talk about the degree of inhibition on the enzyme substrate complex. And so the degree of inhibition on the enzyme substrate complex or the substrate complex or the ES complex is represented as alpha prime, and the prime is this little apostrophe that we see here. And so the degree of inhibition on the enzyme substrate complex alpha prime, of course, is going to quantify the effect that an inhibitor has on the enzyme substrate complex. And so looking down at our image below, notice what we have is the same enzyme catalyzed reaction that we've seen so many times before in our previous lessons. And notice that this time, the inhibitor is affecting the enzyme substrate complex to form the ESI complex. And, of course, we know that anytime the inhibitor is bound to the enzyme like it is here, the reaction is not going to be able to get take place. And so here in this video, what we're emphasizing is that the degree of inhibition on the enzyme substrate complex is represented as alpha prime. And, of course, it's going to be very, very similar to the degree of inhibition on the free enzyme. And so it can be represented as 1 plus this ratio of the concentration of inhibitor over the inhibition constant. But notice that it actually uses the inhibition constant on the enzyme substrate complex k prime I instead of the inhibition complex, the inhibition constant on the free enzyme, k I. And so this k prime I, it's it's gonna correspond with the alpha prime. And so, you might be wondering why is it that we're talking about these degree of inhibitions, alpha and alpha prime? Well, it turns out that both alpha and alpha prime, degree of inhibitions are going to be used as factors to modify the Michaelis Menten and the Lineweaver Burke equations that we're already familiar with from our previous lesson videos. And so alpha and alpha prime will modify these two equations specifically in the presence of inhibitors. And we'll be able to talk more about how alpha and alpha prime can be used as factors in these two equations a little bit later in our course. But for now, this concludes our introduction to the degree of inhibition on the enzyme substrate complex, alpha prime, and we'll be able to get some practice utilizing these concepts in our next couple of videos. So I'll see you guys there.
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Problem
Problem
Calculate the degree of inhibition of an inhibitor on the ES-complex if the [I] = 8 μM and the K'I = 0.03 mM.