in this video, we're going to talk about our third type of reversible inhibition, which is mixed inhibition. Now, of course, mixed inhibition is going to be caused by mixed enzyme inhibitors. And so these mixed enzyme inhibitors actually have mixed binding, since they can actually either bind to the free enzyme, or they could bind to the enzyme substrate complex. And, of course, we know that all enzyme inhibitors, regardless of what type they are, they're all going to decrease the initial reaction velocity or the V, not oven enzyme catalyzed reaction. So no surprise there. And so really, you can think of mixed inhibitors as having some of the mixed features of competitive and uncompetitive inhibitors that we already talked about in our previous lesson videos, since they combined to either the free enzyme like competitive inhibitors and they combined to the enzyme substrate complex like uncompetitive inhibitors. Now, ultimately, the binding of a mixed inhibitor to either the free enzyme or the enzyme substrate complex is going to prevent the conversion of the substrate into the product. And of course, we kind of already knew this as well. Whenever an enzyme inhibitor is bound to the enzyme it's going to inhibit the enzyme by preventing the reaction from taking place Now. What's important to also recognize here is that mixed inhibitors doesn't even mention the word competition at all. And so, with mixed inhibitors, there's absolutely no competition that takes place between the mix inhibitor and the substrate. And so part of this is because mixed inhibitors are actually going to bind to Alice Terek sites on the enzyme, and an Alice Derek site is just an alternative site on the enzyme other than the active site. And since the substrate is binding to the active site and the mixed inhibitor is binding to other sites other than the active site, there's no competition between the two now. What's also important to take into account for mixed inhibitors is that they can actually bind with different affinities to either the free enzyme or the enzyme substrate complex, and recall from our previous lesson videos that the inhibition constant K I is the inhibition constant for the free enzyme that describes the affinity that the free enzyme has for the inhibitor and the inhibition constant on of the enzyme substrate complex, or K prime. I describes the affinity that the enzyme substrate complex has for the inhibitor. And so when it comes to mixed inhibitors, K, I cannot be equal to K prime I meaning that the mix inhibitor will have different affinities to the free enzyme and the enzyme substrate complex. And so, if it turns out that the K I does equal the K prime I, then that is what defines a noncompetitive inhibitor. But we're going to talk about noncompetitive inhibitors later in our course, in a different video. For now, we're gonna focus on these mix inhibitors here where the K I cannot equal k prime I. And so if we take a look at our example down below of mixed inhibition on the left hand side over here, notice what we have at the top is the same exact enzyme catalyzed reaction that we've seen so many times before in our previous lesson videos and notice that when it comes to the mixed inhibitor that the mix inhibitor can actually bind to the free enzyme or to the enzyme substrate complex toe form, the EI complex or the S E complex. And so, in either case, whenever the inhibitor is bound to the enzyme, the reaction is not going to be able to take place. And so notice that the inhibitor binding to the inhibitor for a mixed inhibitor. Uh, it does not compete with the substrate for binding. And so what this means is that the substrate is free to the bind to the enzyme as it pleases, regardless of if the inhibitor is bound or if the inhibitor is not bound. The substrate is always free to bind, and the same goes for the inhibitor. The inhibitor is free to bind to the enzyme, regardless of if the substrate is bound or not. And so that's partly what we mean here by no competition between the mix inhibitor and the substrate for binding. And so over here, on the right hand side, what we have is essentially the same exact thing that we have on the left hand side. Just a different visual representation. And so notice that are free ends. I'm here actually has to binding sites. It has the active site over here, and then it has the mixed inhibitor binding site over here. And so notice that the substrate is free to bind to the active site whenever it is open and available, and the inhibitor is also free to bind to the mixed inhibitor binding site whenever it is open and available. So this allows the mix inhibitor toe bind to the free enzyme. Or it allows the mix inhibitor to bind to the enzyme substrate complex. So here, when the mixed inhibitor is bound to the free enzyme, notice that the substrate is still capable binding to the active site. So, uh, this equilibrium down here is just showing how there's no competition for binding between the, uh, mixed inhibitor and the substrate. However, the most important thing to recognize is that the mixed inhibitor, if it is bound to the enzyme regardless, in what form theme, the reaction is not going to be able to take place. And so again, it's important to note that the mixed inhibitor is going to have a different binding affinity to the free enzyme, uh, to the enzyme substrate complex, meaning that K I will not equal k prime. And so in our next lesson video, we're going to revisit our Scooby Doo analogy and apply mixed in addition to it, as along with giving you guys a memory tool for memorizing thief ex that mixed, uh, inhibitors have. And so this concludes our introduction to mix inhibitors, and I'll see you guys in our next video.

in this video, we're going to talk about the effects that mixed inhibitors have on enzymes. And so it turns out that mix inhibitors may either increase or decrease the apparent K M. And so there are some mix inhibitors that will increase the apparent cam, and there are other mix inhibitors that will decrease the apparent cam. And so later in this video, we'll talk about the exact factors that determine whether a mix inhibitor will either increase or decrease the apparent K M. But all mix inhibitors will always decrease the apparent the mass. And so the real question is exactly how and why is it that mixed inhibitors have these particular effects on an enzyme? And in order to understand that, let's take a look down below at our analogy in this image and notice that we're using the same exact Scooby Doo analogy here for our enzyme catalyzed reaction where he goes and makes a poop on the floor. And so also notice that we're using shaggy here to represent the mixed inhibitor. And that's because we know that shaggy is not very competitive, and that reminds us that mixed inhibitors do not compete with the substrate for binding. Now. One thing that's different between these mixed inhibitors and the uncompetitive inhibitors is that Shaggy here actually has mixed emotions and so notice that Shaggy has the upset emotion with Scoop because he's pooping on his living room couch. And so shaggy here. Onley cares about Scooby when he's bound to that bone. But the shaggy with the mixed emotion over here, uh, he actually loves Scooby Doo so so much that he will actually bind to Scooby Doo even when Scooby is not bound to the bone. And so you can see that when Shaggy binds to the free enzyme version of Scooby, Shaggy will go and give scoop this big old hug. But again, Shaggy is not competitive at all, so he's not going to compete with the substrate in the substrate. Can still bind to the enzyme, could still bind to Scooby. But when it does bind to Scooby, Shaggy is gonna be right there to make sure that Scooby doesn't eat that bone because otherwise he's gonna have to clean up a big old mess. And so, uh, notice that the mix inhibitor combined to either the free enzyme or the mix inhibitor could bind to the enzyme substrate complex. And regardless of which one it binds to whenever the inhibitor is bound to the enzyme. Whether it's in the EI complex or the ES I complex, it's going to prevent the reaction from occurring and prevent Scooby from pooping. And so now that we understand our analogy a little bit better, let's go up to our text and again revisit exactly how and why it is that mix inhibitors have these particular effects. And so first, we're going to look at the effect on the apparent K M. And so it turns out that it's low shot liaise principle that's actually responsible for whether or not the can will increase or decrease. And what is actually going to influence this lush Italy's principal reaction shift is the magnitude of the degree of inhibition on the free enzyme Alfa as well as the degree of inhibition on the enzyme substrate complex, Alfa Prime and so Alfa and Alfa Prime are going to be what dictates the reaction shift of this particular equilibrium right here. And so, if Alfa is greater than Alfa Prime than this, equilibrium is going to shift to the left in this direction this way. And so if the reverse is true of Alfa is less than Alfa Prime, then this equilibrium right here is going to shift to the right. And so if we take a look at our image down below, notice that we have less shot, liaise French flag here, and notice that we have that if Alfa is greater than Alfa Prime, the reaction is going to shift to the right, uh, in this direction. And so notice over here with this, uh, emotion of Shaggy, where he loves Scooby, do we have the Alfa symbol, which is the degree of inhibition on the free enzyme? And so if Alfa is greater than Alfa Prime over here, which is the degree of inhibition on the enzyme substrate complex, then that means that it's the free enzyme that's going to be inhibited mawr. And so that means that the free ends I'm here is going to be decreased. And when the free enzyme is decreased, this equilibrium right here, in order to compensate for the decrease, is going to shift to the left. And so when it shifts to the left, the enzyme substrate complex is going to break down. And when it breaks down the it's gonna make it appear as if the enzyme has a lowered affinity for the substrate. And a lower affinity corresponds with an increased K m. And so when Alfa is greater than Alfa Prime, uh, this corresponds with an increased que en and, of course, the opposite. Over here, when Alfa is less than Alfa Prime, that's going to correspond with a decreased K m. And so if we take a look down below, if Alfa Prime is greater, that means that it's the enzyme substrate complex that will be affected the most. And so the concentration of enzyme substrate complex is going to decrease. And this equilibrium right here, in order to compensate for that decrease is going to shift to the right. And when it shifts to the right, the enzyme substrate complex here is going to form, and that's going to make it appear as if the enzyme has a strong affinity for the substrate, and a strong affinity corresponds with a decreased K m. Just like what we mentioned over here. Now, how is it that you could remember that, uh, these effects here, um caused by the Alfa Alfa prime are going thio increase or decrease the K M Well, in order to remember that we can use this memory tool. So when it comes to mixed inhibition, one of the unique letters of mixed is actually this X here. And so if we rewrite mix, we can actually see that we can use this X on make it look like a greater than or a less than symbol. And so notice that that's exactly what we have right here. Um the X and the mix being a greater than and less than symbol. And so the i n the mix represents an increase, and the D here in the mix represents a decrease, and this is specifically referring to the K M. And so, of course, we're always going to think about Alfa before we think about Alfa Prime. And so if Alfa is greater than Alfa Prime, if Alfa is greater than Alfa Prime like what this box says, then what we're going to get is an increase in the K M. Whereas if Alfa is less than Alfa Prime, like what we see over here than what we're going to get is a decrease in the K M. And so hopefully by using that little memory till that'll help you guys memorize whether or not the K M will be increased or decreased. And so now that we understand a bit better. Exactly, Um, how the K M can either be increased or decreased. Let's move on to the fact that the apparent V max is always decreased. Well, we know that this is actually going to turn out, uh, to be related to the fact that mixed inhibitors are not competitive. And so because mixed inhibitors are not competitive, they cannot compete with the substrate. And that means that it's not possible for the substrate to out compete the mixed inhibitor. And so, since the substrate cannot out compete the mixed inhibitor the effects of the mix inhibitor are not going to be reversed. Uh, even if we increase the substrate concentration to saturating levels and so that decrease in the initial reaction velocity that we know accompanies all enzyme inhibitors is not going to be reversed. And so that's going to correspond with the V Max also being decreased. And of course, since mix inhibitors decrease, the apparent V max. That also means that the catalytic constant or the cake cat or the turnover number is also going to be decreased. And so if we take a look down below at our image right here, notice that we're saying that the catalytic constant, or the cake cat or the turnover number and the presence of mixed inhibitors will be decreased. And that's because the V max is also decreased, whereas the total enzyme concentration stays the same. And so also recall that the reason that the V Max is decreases because if the substrate can't compete, which with mixed inhibitors we know that's the case, then if the substrate can't compete, it can't keep the same V max, so it's going to be decreased. And again, the Onley uh, reversible inhibitor that allows the V Max to stay the same is the competitive inhibitor where s can compete. And so this year concludes our introduction to the effects of mixed inhibitors. And in our next lesson video, we'll talk about how mixed inhibitors affect the McHale is mention plot. So I'll see you guys in that video

So now that we know that mixed inhibitors can either increase or decrease the apparent K M. But they always decrease the apparent V Max in this video, we're going to talk about the effects that mixed inhibitors have on the McHale is meant and plot and so recall from our previous lesson videos that mixed inhibitors have mixed enzyme binding. And that's because mixed inhibitors can either bind to the free enzyme. Or they could bind to the enzyme substrate complex. And because they could do either of these bindings, it's Alfa and Alfa Prime that will both measure its degree of inhibition. Now the Alfa Prime is always going to lead to the decrease of the apparent V max. And so you can see here that the apparent V max is just defined as this ratio of the V Max uhh divided by Alfa Prime. Now it's actually the ratio of Alfa Toe Alfa Prime that's actually going thio either lead to the increase or to the decrease of the apparent K M. And so you can see here, this is how the apparent came is defined. It's defined as Alfa Times, K M over Alfa Prime and So as we discussed in our previous lesson video, the greater the degree of inhibition to the free enzyme relative to the enzyme substrate complex essentially, of Alfa is greater than Alfa Prime. That means that the apparent K M is going to be increased. Whereas if the reverse is true, if Alfa is less than Alfa Prime, then that means that the apparent K M will be decreased. Now, If it turns out that Alfa is exactly equal toe Alfa prime, then that means that the apparent cam is not going to be changed at all. And at that point, the inhibitor is referred to as a non competitive inhibitor. But we're going to talk more about noncompetitive inhibitors a little bit later in our course in a different video. For now, let's take a look at our image down below of these meticulous meant and plots. Now notice over here in the presence of a mixed inhibitor, the McHale is meant. An equation changes as so where the V max is substituted with the apparent V max, which is V Max over Alfa Prime, and the K M is substituted with the apparent km, which is this ratio of Alfa over Alfa Prime Times, K M Now, over here on the right, What we can see is that all enzyme inhibitors, regardless of what type of enzyme inhibitor they are, they're all going to decrease the initial reaction velocity. And so it's clear here that in the presence of these inhibitors here these mixed inhibitors which are the colored, uh, curves here it's clear that the initial reaction velocity is being decreased. And, uh, we also know that, uh, mixed inhibitors always decrease the apparent V max. And so it's very clear that the V Max for these, um, enzymes in the presence of mix inhibitors is clearly decreased. Whereas if we compared to the curve here in the absence of inhibitor, it has a much higher V. Max now also noticed that we have these two curves here. And this curve here in pink is when Alfa is less than Alfa prime. And this curve here in green is when Alfa is greater than Alfa Prime. And so, as we mentioned up above, when Alfa is greater than Alfa Prime, the apparent K M is increased. And so, looking at this green curve right here, looking at the K M noticed that it's actually being increased, uh, in comparison to the black km here in the absence of inhibitor. And so because the K M is being increased, we know that it's true that Alfa will be greater than Alfa Prime for that inhibitor, whereas with this pink curve here, where Alfa is less, an Alfa Prime noticed that there's actually a decrease thio the k m here with respect to the absence of inhibitor. And so, uh, this here concludes our lesson on how mixed inhibitors can affect Mikhail's mention plots and and our next lesson video. We'll talk about how mixed inhibitors affect the line Weaver Burke plot, so I'll see you guys there.

in this video, we're going to talk about how mixed inhibitors affect line. Weaver Berg plots and so recall that way. Back in some of our older lesson videos, we talked about shifting line. We Verburg plots and the skills that we developed in those older lesson videos are actually going to be very useful here in this lesson. And so if you don't remember much about shifting line, we Verburg plots. Make sure to go back and check out those older lesson videos before you actually continue here. Now, that being said, recall from our last lesson video, we said that mixed enzyme inhibitors will always decrease the apparent V max, but they can either increase or decrease the apparent K M, depending on the values of the degree of inhibitions on the free enzyme Alfa and the degree of inhibition on the enzyme substrate complex. Alfa Prime. And so what this means is that mixed enzyme inhibitors can actually change the slope of the line on the line Weaver Burke plot, which is this ratio of km over V max in multiple ways. And so we know that ends mixed enzyme inhibitors air going to decrease the V max. But the K M can either be increased or decreased and not necessarily proportional to the decrease with the V max. And so what this means is that it's possible for mixed inhibitors to increase the slope. But they could also decrease the slope again, depending on the values of Alfa and Alfa Prime. And so, of course, since mixed enzyme inhibitors always decrease the apparent V max, this means that the reciprocal of the apparent V max, which is the why intercept, is always going to be increased. But of course, since the apparent cam can either increase or decrease, this means that the X intercept with negative reciprocal of the camp will either be decreased or increased. And so we take a look at our image down below notice. Over here on the left hand side, what we have is how the line we were Burke equation changes in the presence of mixed inhibitors, and essentially all we need to do is take the reciprocal off the meticulous meant in equation in the presence of mixed inhibitors. And this is what we end up getting. And so over here on the right, in our McHale is in our line. Weaver Burke plot Notice that this black line right here corresponds with the enzyme catalyzed reaction in the absence of inhibitor, so minus concentration of inhibitor. And so if we were to draw in the lines for a mixed inhibitor well, we know that mixed enzyme inhibitors are always going to decrease the V max and decreasing the V max leads to an increase in the Y intercept. And so we know that the Y intercept is going to increase and get further away from our zero marker, which is the Infinity marker. And that means that really, even though the Y intercept is increasing, the V max is decreasing, and so we can go ahead and plot a point up here. So let's put our point here. So that will be the new Y intercept. And then when it comes to the K M, it can either increase or it can decrease. And so that means, of course, that the X intercept will either decrease or increase. And so if the X intercept goes in this direction here, that means that it's getting closer to the zero Infinity marker. And of course, because it's closer to the zero infinity marker. That means that when it goes in this direction, the K M. Itself is actually being increased. And so here's one potential possibility for a mixed inhibitor could look something along this line. So this would be, uh, one possible mixed inhibitor here. Now, the other possibility for the mix inhibitor would be if the k, uh, if the K M. Was instead of being increased, it was being decreased in the opposite direction, getting further away from the zero infinity marker. And so we could put a point over here to represent that, and we could go ahead and say that if it had the same decrease in V Max, it would be there. And so here is another possibility for the, uh, mixed inhibitor and so you can see how the mix inhibitor can actually change the slope. Uh, in multiple ways, it can either increase the slope, but it could also potentially decrease the slope. So you could imagine another situation if we were to draw a red line here where the V Max has only decreased to this point and the K M is decreased to this point. And so you get a line something like this, and that would be a decrease in the slope and another possibility for a mixed inhibitor. So there's a lot of possibilities when it comes thio mix inhibitors and how the effect line Weaver Burke plots. But the main point here is that the KMT's can either increase or they can decrease. But the V Max is always going to decrease. And so this here concludes our lesson to how mix inhibitors can affect line Weaver Burke plots, and we'll be able to get some practice moving forward in our next couple of videos videos, so I'll see you guys there.