Competitive Inhibition

in this video, we're going to talk about our first type of reversible inhibition, which is competitive inhibition. And so, of course, with competitive inhibition, it's going to be caused by competitive enzyme inhibitors, which are actually the most common type of enzyme inhibitors in all of biochemistry. Which is exactly why we're covering competitive inhibitors first, before all of the other different types of reversible inhibitors and so competitive enzyme inhibitors tend to be substrate. Anna logs. And so the question is, what are substrate? Analog? Swell substrate. Analog are compounds that are structurally similar two substrates, and so we'll be able to see that down below in our image as well. Where notice that the inhibitor takes on a shape that is structurally similar to the substrate making competitive inhibitors substrate, Anna logs. And so when it comes to competitive inhibitors, it turns out that the key feature of them is actually the competition. And so competitive inhibitors will actually compete with the substrate for a position in the Free Enzymes active site in order to decrease the initial reaction. Velocity V not of the enzyme catalyzed reaction, but really, that's no surprise to us that the initial reaction velocity has decreased since we know from our previous lesson videos that by definition, all enzyme inhibitors, regardless of what type, are going to decrease the initial reaction Velocity V not of the enzyme catalyzed reaction. And so again, as I've already mentioned, the key feature of competitive inhibitors is actually this competition of how these competitive inhibitors can compete with the sub street. And as we'll see moving forward, none of the other types of reversible inhibitors will actually show this competition. And so this competition factor of competitive inhibitors is quite unique. And so it also turns out it's important to emphasize that these competitive inhibitors will Onley bind to the empty, active sites of free enzymes that are not bound to their substrates. And that's what defines free enzymes. And so because competitive inhibitors Onley affect the free enzymes, that means that Alfa a swell as K I, uh, which are the degree of inhibition on the free enzyme and the inhibition constant of the free enzyme are gonna be the only ones that come into play for competitive inhibitors. And we're not gonna see Alfa Prime or K Prime I for competitive inhibitors. And so we'll be able to talk more about this idea as we move along in our course. But for now, it's just important to note that these competitive inhibitors Onley affect free enzymes and not the enzyme substrate complex. And so, as we'll see down below in our image, these competitive inhibitors will actually block the enzymes active site. And so the substrates cannot bind to the enzyme that's already bound to the competitive inhibitor forming the complex. And so if we take a look at our image down below on the left hand side, we'll see that we've actually seen this image before in our previous lesson videos, and we can see that we have the same exact enzyme catalyzed reaction that we've seen so many times before in our previous lessons and notice that the competitive inhibitor here is represented by I. And it's on Lee affecting the free enzyme here, and it's not affecting the enzyme substrate complex, and so the competitive inhibitor will bind to the free enzyme and form the EI complex. And, of course, when the inhibitor is bound to the enzyme, the reaction is not gonna be be able to proceed, and so we'll get no reaction. And so over here on the right hand side, essentially, what we have is, uh, the same exact, um, reaction. Just a different visual representation of that reaction. And so you can notice here that the free ends on the active site is this little open circle part right here and notice again that the competitive inhibitor is structurally similar to the substrate making the competitive inhibitor a substrate analog. And so what that means is that the competitive inhibitor is going to compete with the substrate for a position in the enzymes active site. If the substrate binds to the enzymes active site first, then that means that the enzyme substrate complex will form. And that means that the substrate is going to be blocking the inhibitor from binding to the enzyme. And that means that if the substrate bind to the enzyme first, that the reaction is going to proceed as normal to form the product. However, if the inhibitor binds to the enzymes active site before the substrate gets there, then the enzyme inhibitor complex will form. And of course, the inhibitor is going to be blocking the substrate from binding. And if the inhibitor is blocking the substrate from binding, then that is going to prevent the reaction from taking place. And so again, the key feature about competitive inhibitors is that they directly compete with the substrate, a feature that we're not going to see again moving forward in our course when we talk about the other types of inhibitors. And so when the inhibitor competes with the substrate, what this means is that they are going to block each other, uh, from binding to the enzymes active site. And again, you can see that the substrate will block the inhibitor from binding, and the inhibitor will block the substrate from binding. And so, uh, in our next lesson, video will introduce an analogy for you guys and some memory tools to help you guys memorize the effects that competitive inhibitors have on enzyme. So I'll see you guys in our next video

in this video, we're going to talk about the effects that competitive inhibitors have on enzymes. And so recall from our previous lesson videos we mention that competitive inhibitors will actually make the apparent km of an enzyme worse and by worse. What we mean is that it's going to decrease the enzymes affinity for the substrate. And of course a decreased affinity corresponds with an increase in the apparent K. M. And so it's true that competitive inhibitors increase the apparent km of an enzyme. But also recall from our previous videos that competitive inhibitors actually do not affect the apparent V. Max of an enzyme. And so the real question here is exactly how and why is it that competitive inhibitors have these particular effects on an enzyme? So, if we take a look at the left hand side over here, notice that this image represents an analogy for our enzyme catalyzed reaction. And notice that this adorably cute little puppy over here represents our free enzyme. And this cute little puppy's name is actually is I'm which is short for enzyme. And then over here, what we have is a bone to represent our free substrate. Now, of course, recall from our previous lesson videos that the substrate will bind to the enzyme, specifically at the enzymes active site. And so in this analogy, the dog's mouth represents the enzymes active site. And so when the bone binds to the dog's mouth as it is over here in this image, it represents the enzyme substrate complex. And then of course the dog can eat the bone catalyze the reaction unaltered while creating this nasty poop over here on the ground. Now, I know talking about poos is a little weird and I can pretty much guarantee you that your professors are not going to relate adorably cute little puppies nor their nasty poos to enzyme catalyzed reactions or these reversible inhibitors. However, this a now right here is going to be incredibly helpful and incredibly useful for us as we move forward and talk about all of the different types of reversible inhibitors and the effects that those reversible inhibitors have, including helping us to understand the competitive inhibitor effects. And so speaking of competitive inhibitors, notice in our image down below, we're using the soccer ball, which is the ball for a competitive sport to represent our competitive inhibitor. And so recall from our previous lesson videos that the soccer ball or this competitive inhibitor is unique in its ability to compete with the substrate. And again, this competition feature is incredibly unique to competitive inhibitors And moving forward as we talk about all of the other different types of reversible inhibitors. We are not going to see this competition feature again. And so we really want to emphasize this important competitive feature of the competitive inhibitor to compete with the sub street for a binding position in the enzymes active site, which is the dog's mouth here. And so notice when the competitive inhibitor or the soccer ball binds to the active site or the dog's mouth. It will create the enzyme inhibitor complex and that will prevent the reaction from proceeding. And so this is because the substrate simply cannot fit into the active site when the competitive inhibitor is bound. And so again they are competing for the same binding position in the dog's mouth. Now, over here we're showing you the greek symbol, alpha, which you can recall from our previous lesson videos is representing the degree of inhibition on the free enzyme. And so this is just a reminder that the competitive inhibitor will only bind to the free enzyme uh in the active site. Again, the dog's mouth and once again we do not want to lose sight of this competitive nature that is so unique to competitive inhibitors. And so here we're basically highlighting that feature by saying that the substrate and the competitive inhibitor are actually going to compete with each other to bind to the enzymes active site. And so now that we have a general understanding of our analogy, let's go back up to our text to again determine exactly how and why competitive inhibitors have these particular effects. Now we're gonna start with how competitive inhibitors increase the apparent KM. And so the reason that competitive inhibitors increase the apparent KM is because competitive inhibitors will actually decrease the concentration of free enzyme. And so notice down below the competitive inhibitor is going to bind to the free enzyme. And that's exactly why we have this alpha symbol right here. So recall that alpha is the degree of inhibition on the free enzyme. And so that reminds us that the competitive inhibitor will only bind to the free enzyme and it will not bind to the enzyme substrate complex. And so again, uh competitive inhibitors are going to decrease the concentration of free enzyme. And so when the competitive inhibitor binds the free enzyme, it forms the ei complex. But in the meantime it's decreasing the concentration of free enzyme. And of course this equilibrium right here by the shot. Lee's principle is going to respond by shifting to the left And so that's exactly what we're saying up above that, the decrease in the free enzyme concentration causes the K -1 reaction to shift to the left. And so notice that here we have this green arrow to represent the shift to the left. And we also have uh is principal right here and was a french scientist, which is why we have the french flag background behind it blue, white and red. Uh huh. And we have the one here that corresponds with the one in the text up above. So we know that there's going to be a shift to the left in this equilibrium when the competitive inhibitor decreases the concentration of free enzyme. And so if the reaction shifts to the lap that means that the enzyme substrate complex is going to break down into free enzyme and free substrate. And of course this is going to make it appear as if the free enzyme has a weekend affinity for the substrate. And that's what we're saying up above as well that there's a weakened enzyme substrate affinity. And of course, we know that the weekend enzyme substrate affinity corresponds with an increase in the apparent KM. And that's exactly why competitive inhibitors increase the apparent KM. So now moving on to the idea that competitive inhibitors do not affect the apparent max. And this has to do with the unique feature of competitive inhibitors which is their ability to compete. And so the reason that competitive inhibitors do not change the apparent V. Max is because the substrate can actually compete with the competitive inhibitor and because the substrate can compete, that means that by sufficiently increasing the substrate concentration, it's possible for the substrate to out compete the competitive inhibitor. And so we can take a look at our image down below, on the right hand side to see how this idea works a little bit better. And so notice here that we have a large pile of bones, an increase in the substrate concentration. And when we increase the substrate concentration so much we can essentially make the effects of the competitive inhibitor negligible, which is exactly why we have this big X through it. And so when there is this much substrate concentration uh the competitive inhibitor is pretty much not even going to affect the enzyme catalyzed reaction, which means that the enzyme catalyzed reaction will be able to proceed normally when there is this much substrate. And of course uh down below the number two corresponds with the number two here and so we can see that a sufficient increase in the substrate concentration allows the substrate to out compete the competitive inhibitor. And that's going to make the effects of the competitive inhibitor essentially negligible, which is why we crossed it out here. And uh if the enzyme catalyzed reaction can proceed as normal, that means that the V MAx is going to be kept exactly the same. So let's take a moment to imagine if you were our little puppy in this analogy. Yes, soccer balls are cool and all but my gosh, look how many bones there are right here. Our little puppies simply cannot resist all of these bones. And so under saturating So substrate concentrations when there are this many bones, all of these bones can out compete the competitive inhibitor. So that the effects of the competitive inhibitor are negligible, meaning that our puppy is basically going to be ignoring the soccer ball competitive inhibitor. And that means that our puppy will only be focused on this huge pile of bones and the enzymatic reaction will be able to proceed forward as if it weren't being affected at all by the competitive inhibitor. And so under saturating substrate concentrations. Our enzyme can still keep the same V MAx. And so the V max will be kept the same. And so what this means is that our enzyme is going to be able to convert the substrate into product at its maximal rate. And so it will be able to create the maximum amount of poops over a specific period of time. Now the good thing is neither you nor I need to deal with all of these poops that our puppy is producing, however, his owner will need to deal with all of these poops. However, the owner of our puppy is not going to come into play into our analogy until a little bit later in our course in different videos when we're talking about different reversible inhibitors. But for now, now, what we can say here about the competitive inhibitor is that they do not change the apparent B max. And so the apparent B max is able to stay the same again because the substrate is able to out compete the inhibitor under saturating substrate concentrations. And so since the apparent V max is not affected, this also means that the catalytic constant or the K cat or the turnover number will also not be affected. And so, recall from our previous lesson videos that the catalytic constant or the K cat is the maximum efficiency of an enzyme under saturating substrate concentrations. And so notice that number three right here is going to correspond with number three. Down below in our image. And so down below, we're going to recall the equation for the Catalan constant for the K cat. And so recall from our previous lesson videos at the K cat is equal to the ratio of the V. Max over the total enzyme concentration. And so recall that our memory tool for remembering the equation for the K cat is that even though the K cat is not a kitty cat, if it were a kitty cat every now and then we would have to take it to the vet. And so you can see the vet here highlighted can help us remember the equation for the K cat now again, because we've said that competitive enzyme inhibitors do not affect the V. Max and they also do not affect the total enzyme concentration, that means that this ratio will not change. And the K cat or the cattle eat constant also will not be affected. And so this is really a lot of information to remember about the competitive inhibitor effects. And between you and me, who would have ever thought that these adorable, cute little puppies and their nasty poops would help us get an A on our next test. But you learn something new every day. But anyways, this is a lot of information. So how could we potentially memorize these uh important effects that competitive inhibitors have on enzymes. And so that's exactly what this next blue box down below is all about. And so when it comes to competitive inhibition, we know that the unique feature of competitive inhibition is again the ability for it to compete. And again, this is a feature that we're not going to see again moving forward. So we really want to appreciate in take into account this unique feature of competition right here right now with competitive inhibition. And so if we rewrite competitive with a K. It's literally telling us what happens to the K. M. And so we can see that the K. M. Is going to be increased. And so with in the presence of competitive inhibitors, we can say that the K. M. Will be increased. Now, in terms of the V. Max. Again, we want to remind ourselves of the unique feature of competitive inhibition, the ability to compete. So we think about the soccer ball and so we know that the substrate can compete with the soccer ball and so it's possible for the substrate to out compete the soccer ball. And so if the substrate can actually compete, then that means that it can keep the same V. Max. And of course, what this means is that if the substrate cannot compete, then it cannot keep the same V. Max. And so later in our course, we'll see that again, this competition feature is unique to competitive inhibitors. So competitive inhibitors are gonna be the only one that allow for the same V. Max and all of the other reversible inhibitors are going to decrease the V. Max. But again, we'll talk about that as we move forward in our course. For now, you can think if the substrate can compete, it can keep the same V. Max. And so this here concludes our introduction to the effects of competitive inhibitors, and we'll be able to talk about exactly how competitive inhibitors affect the Michaelis menton plot in our next video. So I'll see you guys there.

So now that we know that competitive inhibitors increase the apparent K M but do not affect the apparent V Max in this video, we're going to talk about how competitive inhibitors affect the McHale is meant in plot. And then later in a different video, we'll talk about how competitive inhibitors affect line. Weaver Burke plots and so recall from our previous lesson videos, we said that all enzyme inhibitors, regardless of what type they are so including competitive inhibitors, they are all going to decrease the initial reaction velocity or the V, not of an enzyme catalyzed reaction. And so notice down below in our image. On the left hand side, this Mikhail is meant in plot shows, two different curves. This black curve here represents the enzyme catalyzed reaction in the absence of inhibitor indicated by minus concentration of I. In this blue curve represents the enzyme catalyzed reaction in the presence of competitive inhibitor indicated by plus concentration of I and notice that in the presence of competitive inhibitor, if we focus on the initial reaction rate or the V not, it's actually decreased. As we mentioned in our previous lesson videos and up above and so also recall from our previous lesson videos that competitive enzyme inhibitors Onley bind to the free enzyme, which means that Alfa is going to measure the degree of inhibition on the free enzyme. And so the degree of inhibition on the free enzyme Alfa of a competitive inhibitor is on Lee going to increase the apparent K M, as we already know from our previous lesson videos. And so in the presence of competitive inhibitor, the apparent K M is defined as the degree of inhibition on the free enzyme Alfa Times, the K M. In the absence of competitive inhibitor and also, as we know from our previous lesson videos, competitive inhibitors do not change or affect the apparent fee max, which means that the apparent V Max is equal to the V Max in the absence of inhibitor. And so notice down below. On the left hand side, we're showing you guys the McHale is meant an equation that we already covered in our previous lesson videos. And so this is the McHale is meant in equation in the absence of any inhibitors, and so if we want to get the McHale is meant an equation in the presence of a competitive inhibitor. Then all we need to do is take the K M and substituted with the apparent km, which is Alfa Times K M. So that's what we have down below. And then take the V max and substituted with the apparent V max, which is equal to just the V max. So notice we didn't change it down below. And so this equation here represents the McHale is meant an equation in the presence of competitive inhibitor. And so, again, taking a look at this Michaela Schmitz and plot right here notice that even in the presence of competitive inhibitor that the V Max is not changed. And so the Blue Curve and this black curve both have the same exact V Max. And so again, that shows that the V Max is not changed. And so recall that the substrate concentration can be represented as bones from our previous lesson video. And so if we increase the concentration of bones, eventually we'll get to ah, high enough concentration of bones where Scooby Doo is going to completely ignore that competitive soccer ball inhibitor. And that means that Scooby Doo is gonna be able to produce the maximum amount of poops on the floor. And so, of course, this shows that, uh, with competitive inhibitors the substrate, the amount of bones can compete to keep that same V Max. However, even though the V max has not changed, if we focus on the k m. Notice that the K M is changed here. So the K m in the absence of inhibitor with this black line here, notice is lower than the apparent km for this blue curve here in the presence of competitive inhibitor. And this means that the apparent km was increased in the presence of the competitive inhibitor. And so pretty much what we're seeing is, uh, the effects of competitive inhibition on the McHale is meant in plot. And so over here on the right, this Michaela cement and plot, all we're trying to show you is the effect of increasing the concentration of competitive inhibitor and so notice that we have three curves. Here we have this black curve here that again represents the enzyme catalyzed reaction in the absence of inhibitor indicated by minus concentration of I. And then we have this purple curve here that represents the enzyme catalyzed reaction in the presence of just plus one Moeller concentration of competitive inhibitor and notice that the K M increases further here and notice that the green curve here represents the enzyme catalyzed reaction in the presence of even Mawr competitive inhibitor. So, plus two Moeller concentration of competitive inhibitor. And so by increasing the concentration of competitive inhibitor, even MAWR notice that the K M is increased even further. And so you can see that the effect of competitive inhibitors is that they're going to increase the K M. And the more competitive inhibitor we add, the greater the K M will be increased. But notice that no matter how much competitive inhibitor we add, the V Max is going to be unaltered. And again. That's because if we increase the amount of bones eventually, we'll get to a concentration of bones where Scooby Doo is going to completely ignore that competitive inhibitor and produce the maximum amount of poops on the floor. And so this year concludes our lesson on how competitive inhibitors affect the Makayla Smith and plot. And in our next lesson video, we'll talk about how competitive inhibitors affect the line. We were burke plot, so I'll see you guys in that video

in this video, we're going to talk about how competitive inhibitors affect line weaver bird plots and so recall that way back in some of our older lesson videos, we talked about shifting line we Verburg plots. And so a lot of the skills that we developed and concepts that we learned in those older lesson videos are actually going to be very important for this lesson video. And so, if you don't remember much about shifting line Weaver Burke plots, make sure to go back and check out those older lesson videos before you continue here. Now, that being said also recall from our previous lesson videos that the slope of the line on a Line Weaver Burke plot or A. L. W. Burke plot for short. It's just this ratio here of the K M over the V Max, and we know that competitive enzyme inhibitors do not affect the V max, but they do increase the K M. And so ultimately, that's going to lead to an increase and the slope of the line on the line with Herbert plot when we add even mawr competitive inhibitor and so the mawr competitive inhibitor that we add the steeper. The line on the line with Herbert plot will become. And it's also important to note that the line Weaver Burke plot is also known as a double reciprocal plot. And that's because it plots the reciprocal of the initial reaction Velocity V not on the Y Axis. And it plots the reciprocal of the substrate concentration on the X axis. And we also know that the line Weaver Burke plot is directly related to the line Weaver Burke equation, which resembles the equation of a line. Why equals M X plus B. And so if we want to get the line we were Burke equation in the presence of a competitive inhibitor, then all we need to do is take. The McHale is meant in equation in the presence of a competitive inhibitor and take the reciprocal of that equation. And when we do that, what we get is the line Weaver Burke equation in the presence of a competitive inhibitor. And so we also need to recall that on a line Weaver Burke plot, the most important information about an enzyme is revealed through the intercepts and so recall that the why intercept is the reciprocal of the V max and the X intercept is the negative reciprocal of the K M. Now, because competitive inhibitors do not affect the V max, the V max stays exactly the same. That also means that the why intercept or the reciprocal of the V max is also not going to be changed. However, the X intercept because it's the negative reciprocal of the K M. Uh, ultimately, because competitive inhibitors increase the K M itself. So it's going to be increased because again it plots the reciprocal of the substrate concentration. The X intercept magnitude is going to be decreased. And so if we take a look at our image down below of this line, we have Robert plot right here. Notice we have these two different lines. We have this black line here that represents the enzyme catalyzed reaction in the absence of inhibitor indicated by minus concentration of I. And then we have this purple line here that represents the enzyme catalyzed reaction in the presence of one concentration of competitive inhibitor, essentially one Moeller concentration. And so notice that the why intercept, which is where these two lines cross the Y axis does not change. It's exactly the same for both lines. And that's because again competitive inhibitors do not affect the V Max. The V Max stays the same, which means that the Y intercept is also not gonna be change. It's going to stay the same, just like what we see down below. However, we know that in the presence of competitive inhibitors, the K M is going to be increased, and an increase km means that it's going to be shifted towards closer towards the zero marker, which we know acts as the infinity marker for the K. M. And so notice that the K M is shifted to the right for the Purple Line and the presence of competitive inhibitor on DSO. Now the X intercept is closer to the zero infinity marker. And so that means that the K M is larger when it's closer to this zero infinity marker. And so ultimately, the magnitude of the X intercept is being decreased. But the K M itself is being increased, and so by magnitude, essentially, what we're saying is that the value itself, when we're disregarding the negative sign is getting smaller. And so notice that the example here is asking us specifically to draw the representative line for the enzymes activity if the concentration of competitive inhibitor was double. And so if we increase the concentration so that it is plus two concentration of inhibitor, essentially the line is going to become even mawr steep. It's going to become steeper. And so, of course, we know that the V Max is going to say the same. So the why intercept is also not going to be changed. So this eyes going to stay the same and, of course, the Azaz. We increase the concentration of competitive inhibitor to double the K. M is also going to get greater and get closer to the zero infinity marker. Essentially, this green line right here represents, uh, the enzyme catalyzed reaction activity in the presence of double the concentration of competitive inhibitor. And so this here concludes our lesson on how competitive inhibitors affect line Weaver bird plots and as we move forward in our course, will be able to get some practice utilizing the concepts that we've learned. So I'll see you guys in our next video