hopefully you have already watched the Con Academy videos on in inhibition kinetics so looking at the different types of um inhibitors for an enzyme we're going to summarize some of the things that you learned in that video but you do need to make sure that you've watched that video and taken appropriate notes all right let's look at our inhibition kinetics the first type of enzyme we looked at was that competitive inhibitor so these are figures from your text here is our active site of our enzyme and and it would normally b a substrate to make that enzyme substrate complex and then give us our enzyme plus our product at the end and remember we talked about how the reverse Rea or the Con Academy videos talked about how that reverse reaction essentially does not happen so we can draw a single-headed arrow in this now if we have a competitive inhibitor it is binding to the active site so here is our competitive inhibitor and so now we have to worry about the fact that our enzyme is no longer going to be able to bind substrate it is competing for the active site of this protein in this middle figure here we're looking at our velocity of our enzyme versus our substrate concentration our blue line here is looking at our free enzyme so this is enzyme with no inhibitor present so that's why it says minus I so we can see our km value would be here so that is the concentration at which we get half of our maximum velocity and we have our V Max our theoretical V Max up here our red line is our enzyme with inhibitor so one thing I want you to notice is that we eventually reach the same Vmax but it happens at a much higher substrate concentration and that's because we have to add more substrate to overcome the effects of the inhibitor so Vmax Remains the Same however it's going to take more substrate in order to overcome the inhibitor that you've added because of that our km apparent is going to increase because it requires more substrate in order to get half your maximum velocity when we put it into a line Weaver Burke equation so we have one over the velocity and one over the substrate we can see that our um our Y intercept for which is one over our Vmax is the same because again our Vmax concentration does not change but our 1 over our km does change and our slopes change because that km value or that km apparent changes when we add our um inhibitor so since we have to add more inhibitor our slope is going to be higher in this case but our x intercept is going to be much lower all right this is an example of a competitive inhibitor um this competitive inhibitor is um catril catril which is a Statin drug so this is going to inhibit the enzyme that is used for the synthesis of cholesterol so this would be a drug that we you would use in order to lower your cholesterol level so that is the general class of what statins do uh so in this enzyme uh we have a co-actor here a co-enzyme which is a zinc ion and this black molecule here is this drug catpro and so you can see that is interacting with the zinc it's also interacting with some um other so we got some histadine here a tyrosine in our active site in the second figure they're overlay where catril uh interacts and where the normal substrate Angiotensin reacts and so we can see Angiotensin in Gray and catril in Black are in the exact same position so they're both they would both interact in the active site now they do not both go into the active site normally they are overlaying their positions into this figure to show you that they are um they work in the exact same spot of the protein so this would be a competitive inhibitor when you add catril now Angiotensin is not able to bind to the active site of this enzyme all right let's look now at our uncompetitive Inhibitors now the video only talked about the uncompetitive Inhibitors to the left but your book also talks about another type of uncompetitive Inhibitors which is shown on the right so in your uncompetitive inhibitor you've got your enzyme with a substrate and now you form this enzyme substrate complex and how the typical uncompetitive inhibitor is going to work is that it's going to bind to a second spot of the protein which is going to change the protein confirmation and not allow the substrate to be released as as product so it's not going to affect the ability of your substrate to bind your enzyme your substrate is still going to bind your enzyme just like normal but what it will affect is your substrate being to turn over into product so this enzyme inhibitor substrate now cannot have a reaction this second type of uncompetitive inhibitor is looking at when you have a reaction that requires two different substrates in order to bind so the first sub substrate binds just fine and then you might have a second substrate that will'll need to bind and then those two substrates might combine to form your product or do some other sort of reaction so if you bind an inhibitor in this case after your first substrate has bound this inhibitor would be an uncompetitive inhibitor of substrate one however now substrate 2 is not able to bind to this enzyme complex because this inhibitor is in place so this substrate this inhibitor would be a competitive inhibitor for substrate 2 but when we're looking at the enzyme kinetics it would act as an uncompetitive inhibitor for substrate 1 and competitive for substrate 2 all right let's look at our uncompetitive Inhibitors in terms of our um our velocity versus our substrate concentration so one thing that we can see that is different here is that as we're looking at our uncompetitive Inhibitors our Vmax is going to be lower for our inhibitor and because if we go back and look at our mechanism uh once we have added the substr at when we have inhibitor present we are not turning it into product that means that the amount of substrate that we have to add in order to reach our maximum velocity is going to be decreased and it's going to be decreased because we don't need to add as much substrate um as we're not going to be able to turn over into product so our Vmax is going to be higher when we have no inhibitor and it's going to be lower when we do have an inhibitor we look the Vmax in hence the km value we'll see that when we have an inhibitor the K the V Max is going to be lower which means that our substrate concentration at which we get the 1/2 Vmax will also be lower now they're going to the Vmax and the km will both be lower by the same factor which is this 1 over Alpha because they're both lower by the same factor their ratio of KM to V Max is the same so the slope of when we're looking at our line Weaver bur the slope of our lines in each case remains constant because your km and your Vmax are both changing by that same factor um but when we're looking at this we can see that our y intercepts are different our X intercepts are different as well for uncompetitive Inhibitors all right let's look now at an example we've got this uncompetitive inhibitor this is um the drug is Methotrexate this is an anti-cancer agent and it is an uncompetitive inhibitor of dihydrofolate reductase so this enzyme here is that is the enzyme of dihydrofolate reducta so dihydrofolate would be the substrate and we would be reducing it in this enzyme so it's going to bind tightly to the substrate complex and so now it is no longer um able so we've got the substrate here in purple we've got the drug here in Black it is no longer able to bind the nadp H which is going to be necessary to reduce it um and thus it is an uncompetitive inhibitor of this enzyme so last we that mixed inhibitor case and this is where your inhibitor can bind either to your enzyme without substrate or to your enzyme with substrate and in in this case because it's a mixed inhibitor we see um we see a little bit of both we see some competitive inh inhibition and some uncompetitive inhibition I like the the term mixed inhibitor better than what the Con Academy video used which is that non-competitive because non-competitive and uncompetitive sound awfully similar but we're going to just refer to this as a mixed inhibitor so in this case we can see that we've got varying slopes uh because it's not a straight uncompetitive inhibitor it can um affect The Binding of your substrate uh so we're going to see changes in both the V Max and the km and they're not going to be equal changes because of that