Enzyme Kinetics with Michaelis-Menten Curve | V, [s], Vmax, and Km Relationships

so often with enzymes you'll also be dealing with enzyme kinetics and remember that kinetics deals with rates and how rates are affected when you change the concentrations or amounts of different components and so when you're dealing with enzyme kinetics what you'll often be looking at is how the rate of an enzyme-catalyzed reaction will change as you change the level of substrate present in your environment and usually a discussion of enzyme kinetics will show up on a michaelis-menten plot and this plot is one that has the velocity or you could say the rate at which the reaction proceeds as its y-axis and the concentration of substrate as its x-axis and so by looking at a graph like this we can glean important information that tells us about various characteristics of this enzyme and substrate one thing to realize when you're dealing with a plot like this is that this plot is for a specific amount or concentration of enzymes so if you had a lot more enzyme present this plot would look different and some of these points might change so realize that any one of these plots is for a specific amount of enzyme being present within a reaction environment when you're working with a plot like this there are two very important points to be aware of and which can help you figure out how the reaction changes and what kinds of activity are going on if for example a competitive or non-competitive inhibitor appears those will have different effects on these things v max and km and so we'll go through these two components and then in a later video what we'll do is we'll go through how these change in the presence of a competitive or non-competitive inhibitor so the v max is the maximum velocity which essentially means the maximum rate at which a reaction can occur given this amount of enzyme concentration and so the v max will be this point you could say it's an asymptote of how high the curve goes so that no matter how much substrate you add it will never exceed this level here so this point here is known as the vmax and that just tells you the maximum potential or you know the maximum ability or capacity of the enzyme at whatever given enzyme concentration you have so vmax is this high point where you can add more substrate but you don't see any more increase in the reactivity notice that it starts very low because when you're at a very low substrate concentration there just isn't that much substrate and even if there is some amount of substrate it's hard for the substrate to find an enzyme and so we'll get into km and how that discusses affinity but just realize that at low substrate concentrations your reaction is going to go more slowly and as you increase the substrate not only is there more substrate but it also means that there's more substrate that's likely to find a free enzyme and so that's why you see this direct relationship of substrate concentration being proportional to the velocity of the reaction then when you have v max the next thing to do is find one half v max so one half v max is fairly straightforward it's just the point where you are now at a velocity of reaction or a rate that is half of the maximum velocity and one half v max isn't all that important by itself but it can be important because it helps you find a quantity that is very useful and that quantity is known as km km is also known as the michaelis-menten constant and notice that it is on the x-axis here because it is the concentration of substrate where you see the velocity being at half of the maximum velocity and if you're comparing relative km values you can often look at those in order to figure out the affinity of a substrate for its enzyme or of this an enzyme for its substrate so let's just draw a different curve here and we'll kind of see an illustration of this notice that these here have a the same vmax they both max out at the same point but if you're going to look at the half vmax the km value will be greater in this second curve so the km value will increase when there's less affinity and so this brings us to a relationship that um a high km means a low affinity the better the affinity is meaning the better that the substrate is at finding an enzyme the more quickly you're going to get to half v max so if your km is down here for example with a rapidly rising curve maybe something like that then what you'll see is that this means that the substrate is very good at finding that enzyme and so it's a very very high affinity substrate so what km tells you is that if you're at a lower km that means that the enzyme substrate complex has a very high affinity it's easier for the substrate to find that enzyme and thus it's going to move closer to its maximum capacity a lot more quickly so you've got vmax which is the top point where you no matter how much substrate you add you will not see an increase in the rate because essentially all available enzymes are going to be saturated it's saturated because every enzyme is busy participating in the reaction and as soon as it becomes a free enzyme there's enough substrate available that it will just automatically fill that spot and continue the reaction so it's the saturated or maximum velocity of this particular enzyme concentration and a lot of the substrate being around the km value is something that reflects the affinity with which the substrate binds its enzyme and the lower the km is the better affinity your substrate has for its enzyme and remember that km or the michaelis-menten constant is the substrate concentration realize that it's a concentration of substrate which is why it's on your x-axis it's the substrate concentration where you reach this level one-half v-max one-half v-max by itself isn't very useful v-max is but one-half max can be helpful for finding km which tells you about a lot of the properties of this enzyme substrate complex and so in addition to helping us figure out the maximum velocity with which a reaction can occur at a given concentration of enzyme and the affinity with which the enzyme binds its substrate these values are also useful when we are in the presence of an inhibitor and there are different types of inhibitors there are competitive inhibitors ones which compete with the substrate to bind that active site so competitive ones compete with the substrate to bind that active site and thus slow down the ability of the enzyme to do stuff with the substrate because it's being distracted by the inhibitor and there's non-competitive inhibition which doesn't have to do with fighting over that active site but instead it has to do with an inhibitor that makes the enzyme less capable of catalyzing this reaction and so these things will change and so you so in a in our next video we'll go through how in the presence of a competitive inhibitor certain things will happen with vmax and km whereas in the presence of a non-competitive inhibitor these will behave differently certain quantities behave differently the k m and v max will respond differently in the presence of competitive inhibitors versus non-competitive inhibitors and we'll go through all the nuances of analyzing that and being able to look at two different plots and seeing what's going on whether it's competitive or non-competitive and using this in order to analyze the type of enzyme activity going on but before we get there it's really important to recognize that v max tells you the absolute maximum capacity that any concentration of enzyme is capable of conducting these reactions and to realize that km is a substrate concentration it's on the x-axis and it is related to when you find one-half vmax and the km can tell you very important things about the substrate enzyme affinity so now we'll move into a discussion of enzyme kinetics and the different curves that those will present when you're in the presence of different inhibitors competitive versus non-competitive inhibitors

Channel: PremedHQ Science Academy

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Id: kmyR1cYxRL4

Length: 9min 54sec (594 seconds)

Published: Sun Dec 20 2015