In this video, we're going to do a recap of reversible inhibition, and so because this is a recap of all the common types of reversible inhibitors that we already covered in our previous lesson videos, really, there's no new information in this video, which means that if you already feel like an expert on these reversible inhibitors, then feel free to skip this entire video since really there's no new information. But if you're struggling with these reversible inhibitors even just a little bit, then this video could potentially be very valuable for you.

And so recall that the 4 different types of reversible inhibitors that we already covered are competitive, uncompetitive, mixed, and noncompetitive inhibitors. And so notice down below in this table, we have information on all 4 of these different types of reversible inhibitors organized into these rows. And so the first row has competitive inhibitors, the second row has uncompetitive inhibitors, the next two rows are for mixed inhibitors, and then the last row is for noncompetitive inhibitors. And notice that the mixed and the noncompetitive inhibitors have the same exact pink background. And that's because recall that noncompetitive inhibitors are really just a type of mixed inhibitor. And so, notice that there's a lot of information here in this table, but really all I want you guys to focus the most on is this last column here, the overall effect that the inhibitors have on the enzyme.

And so, first, we're gonna focus on filling out the overall effect on the Vmax for each of these inhibitors, and then we'll cover the KM. And so, looking at this first row here for competitive inhibitors, recall that the unique feature of competitive inhibitors is that they can actually compete with the substrate whereas all of these other reversible inhibitors cannot compete with the substrate. And so because competitive inhibitors can compete with the substrate, this means that it's possible for the substrate to outcompete the competitive inhibitor and completely negate its effects. Meaning, it can make the effects of the competitive inhibitor negligible when we increase the concentration of substrate a lot. And so that means that the Vmax is going to be unaltered, meaning that the apparent Vmax is going to equal the Vmax. And so, for the overall effect here of competitive inhibitors on the Vmax, we can simply write in not changed. Now, again, the Vmax not being changed here is a unique feature of competitive inhibitors because it turns out that with all of the other reversible inhibitors, the Vmax is actually always going to be decreased, and so we can represent decreased by drawing in down arrows. And so, that's pretty easy to remember, isn't it? Notice that only the competitive inhibitor is not changed, but all of the other reversible inhibitors, the Vmax is decreased. And so recall that if the substrate can compete, then it can keep the same Vmax. However, if the substrate cannot compete, then it cannot keep the same Vmax and the Vmax will be decreased.

And so, now moving on to the overall effect on the KM, recall that competitive inhibitors only bind to the free enzyme. And so alpha is going to represent its degree of inhibition. And notice that the apparent KM here, is equal to alpha times KM and we know that alpha must be always greater than or equal to one, which means that as we increase competitive inhibitor, the KM can only be increased. And so, what we can do is we can write in an up arrow here, to represent that the KM is increased in the presence of a competitive inhibitor. Now, moving on to uncompetitive inhibitor, recall that the unique feature of uncompetitive inhibitors is this u here, which reminds us of a u-turn going downwards, which reminds us that not only is the Vmax gonna be going downwards, but so is the KM. And so, we recall that the uncompetitive inhibitors, unlike competitive inhibitors, they only bind to the enzyme substrate complex, which means that alpha prime, describes its degree of inhibition. And notice that the apparent KM is, equal to KM over alpha prime. And so alpha prime, can only be greater than or equal to 1, which means that as we increase uncompetitive inhibitor, the KM will be decreased as we already indicated. And, of course, the Vmax, is also going to be decreased as well since, it's the same, Vmax over alpha prime. And so, looking down, notice that all of the apparent Vmaxes for all of these reversible inhibitors here, are exactly the same, leading to the same result in the Vmax being decreased.

And so, now moving on to the mixed inhibitors, recall that mixed inhibitors have mixed some of the features of competitive and uncompetitive inhibitors because mixed inhibitors can bind to either the free enzyme or the enzyme substrate complex, which means that both alpha and alpha prime describe its degree of inhibition. Now, mixed inhibitors, depending on if alpha is greater than alpha prime or if alpha is less than alpha prime, they could either increase or decrease the KM. Now if alpha is greater than alpha prime, that's going to lead to an increase in the KM represented by an up arrow. And so, you can see that here as well. If alpha is greater than alpha prime, then that means that this ratio right here will be greater than 1 and anything greater than 1 multiplied by the KM is going to make the KM greater. However, if the alpha is less than alpha prime, that means that alpha, on top will be less than alpha prime making this ratio smaller than 1, essentially a fraction and a fraction times KM is going to make the KM smaller. And so, we can put in a down arrow here. And so, if we move on to our next inhibitor, the noncompetitive inhibitor, again, recall that it's a type of mixed inhibitor where, the degree of inhibition on the free enzyme alpha is exactly equal to the degree of inhibition on the enzyme substrate complex alpha prime. And so if alpha is exactly equal to alpha prime, then this entire ratio is going to be 1 and one times the KM is,