6. Enzymes and Enzyme Kinetics
Michaelis-Menten vs. Lineweaver-Burk Plots
Michaelis-Menten vs. Lineweaver-Burk Plots
Was this helpful?
in this video, we're going to do a little compare and contrast between the McHale is meant in plot and the line Weaver Burke plot. And so it's important to note is that if multiple enzyme kinetic variables are missing or just completely unknown, then we cannot use the equation form of either the meticulous meant in equation or the line we were Burke equation. However, we can still determine these enzyme kinetic variables such as the V max, and the McHale is constant, k M, uh, graphically, so we can determine them graphically via plotting enzyme kinetic experimental data onto a meticulous meant in plot or a line Weaver Burke plot. And so, as we'll see down below in our image will see that a line Weaver Burke plot actually provides some graphical advantages over the meticulous meant in plot. And so if we take enzyme kinetic experimental data and graphically plot that enzyme, kinetic experimental data onto a McHale is meant in plot, then we can Onley approximate. We can Onley approximate the values of the V Max and the K M. However, if we take that same exact enzyme, kinetic experimental data and graphically plot that data onto a line Weaver Burke plot. Instead, we can actually get a more accurate measurement of both the V Max and the K M. So let's take a look down below at our image to clear up some of this, uh, idea. And so notice on the left over here. What we have is our Michaelis meant in plot and on the right over here, what we have is our line Weaver Burke plot. And so starting with the McHale is meant in plot. Over here. Notice we have the same plot that we've seen so many times before and our previous lesson video. So on the y axis notice we have the initial reaction velocity or the initial reaction rate V not on the x axis. Notice that we have the substrate concentration. And of course, we can see that we have this same rectangular hyperbole. A curve that we get for so many. McHale is meant in enzymes. And so notice that RV max is represented as a horizontal Assam tote on this plot, and the McHale is constant. K M is an exact substrate concentration that allows for the initial reaction velocity to be equivalent to exactly half of the V max or V Max over to. And so, essentially, what you'll notice is that if we were to take enzyme kinetics experimental data, let's say that we had five experiments. Let's say that we had our first experiment at low substrate concentration. And then we measured the initial reaction velocity, and that data point came out right here. And so essentially, we took a higher substrate concentration, and we plotted the initial reaction velocity, and that came out right here. And then we took another, higher one, and that came out over here. And then we took another one that came out up here, and then we took a different one, and that came out over here. So those are our five experimental data points that we plotted here and from these five experimental data points notice that they don't not make a perfect curve. If we were to connect these lines, they don't really make a perfect curve. However, if we were to get a curve of best fit here, then we would be able to get this, um, rectangular hyperbole, a curve that we see so many times in so many different, uh, graphs. McHale is meant in grafs. However, what you'll note is that of these five different experiments really Onley Two of these experiments are contributing to this horizontal plateau of our graph here, which is really the horizontal plateau where the initial reaction velocity is approaching the V max and these other data points that we have here these other experimental data point they're not really contributing toe helping us determine where this horizontal plateau is. And so these data points here are not helping us determine the V max of our enzyme. And so, for that reason, what we end up getting is an inaccurate measurement of the V Max That's again obtained by estimating where this initial reaction velocity, uh, curve levels off and again it's leveling off here at this green region. Um, and it's approaching the V max at this green region. And so because we have less data points, we only have two of the five total experimental data points helping us, uh, contribute to where this V max value is. Um, that's not all of the data points contributing. And so, since there's less data points, that's why we get on inaccurate measure. And so because the K M is associated with half of the V max and we're getting an inaccurate measure of the V. Max. Uh, that means that we're also going to get an inaccurate measure of half of the V max. And that means that we're also going to get an inaccurate measure of the K M from using. Ah, McHale is meant in plot. However, now, if we take a look at our line Weaver Burke, plot on the left again recall that a line with Herbert plot is also known as a double reciprocal plot. Because the Y axis is the reciprocal of the initial reaction velocity. And the X axis is the reciprocal of the substrate concentration. And so when we plot the reciprocal, uh, noticed that our data is going to form Ah, line of best fit. So when we plot our five experimental data points on this plot, we would have five points. Uh, that would all be essentially falling onto this same line. And so all five of these experimental data points are helping to contribute to this line of best fit on this line of best fit is going thio determine the X the y intercept here, Um, as well as the X intercept down here. And so because the why intercept here is associated with the V Max. What we can say is that we have all five of our experimental data points are helping to contribute to the value of the Y intercept and therefore the value of the V Max. Instead of having just two data points contribute, we're having all five of the data points contribute to the value of the V max and the more data points we have contributing to the value of the V max, the more accurate RV max value is going to be so from plotting the same exact experimental data onto a line Weaver Burke plot were able to get a more accurate measurement of the V max obtained from the why intercept, which again is shown by this red point here and also noticed that the K M uh is going to be associated with the X intercept. And all five data points are also contributing to the value of the K M, which can be separately determined from the value of the V Max because the K M can be accurately determined from the X intercept all on its own. And so, essentially, what we can see here is that by plotting our enzyme kinetics experimental data onto a line, Weaver Burke plot were able to form a line where all of the data helps to contribute to the value of the V Max and the value of the K M. And so the ah line Weaver Burke plot will help us get a MAWR accurate measurement of both the V Max and the K M. In comparison to ah, McHale is meant and plot. And really, that's the main take away of this video, and we'll be able to apply the concepts that we've learned here in our practice problems, so I'll see you guys there.
Why is it preferable to use a Lineweaver-Burk over a Michaelis-Menten plot when studying enzyme kinetics?
To directly visualize Km & Vmax on the plot.
To plot kinetic data as a hyperbolic curve instead of a line.
To obtain a more accurate measure of the V0.
To remove terms that cannot be calculated in a typical enzyme kinetics experiment.
To get more accurate estimates of Km & Vmax.
You measure V0 of an enzyme at 6 different [S] & plot the data on a Lineweaver-Burk plot. You then determine the line of best fit to the data to visualize the x & y intercepts. Calculate the Vmax & Km of the enzyme. Hint: pay close attention to the indicated units.
Was this helpful?