Michaelis-Menten vs. Lineweaver-Burk Plots - Video Tutorials & Practice Problems
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Michaelis-Menten vs. Lineweaver-Burk Plots
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Video transcript
In this video, we're going to do a little compare and contrast between the Michaelis Menten plot and the Lineweaver Burk plot. And so what'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 Michaelis Menten equation or the Lineweaver Burk equation. However, we can still determine these enzyme kinetic variables such as the vmax and the Michaelis constant Kilometers, graphically. So we can determine them graphically, via plotting enzyme kinetic experimental data onto a Michaelis Menten plot or a Lineweaver Burk plot. And so as we'll see down below in our image, we'll see that a Lineweaver Burk plot actually provides some graphical advantages over the Michaelis Menten plot. And so if we take enzyme kinetic experimental data and graphically plot that enzyme kinetic experimental data onto a Michaelis Menten plot, then we can only approximate we can only approximate the values of the vmax and the kilometers. However, if we take that same exact, enzyme kinetic experimental data and graphically plot that data onto a Lineweaver Burk plot instead, max and the k m. 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 idea. And so notice on the left over here what we have is our Michaelis Menten plot, and on the right over here what we have is our Lineweaver Burk plot. And so starting with the Michaelis Menten plot over here, notice we have the same plot that we've seen so many times before in our previous lesson videos. So on the y axis, notice we have the initial reaction velocity or the initial reaction have this same rectangular hyperbola curve that we get for so many Michaelis Menten enzymes. And so, notice that our vmax is represented as a horizontal asymptote on this plot and the Michaelis constant Kilometers 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 2. And so, essentially, what you'll notice is that if we were to take ex enzyme kinetics experimental data let's say that we had 5 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 5 experimental data points that we plotted here. And from these 5 experimental data points, notice that they do 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, rectangular hyperbola curve that we see so many times and so many different different graphs, Machlis Menton graphs. However, what you'll note is that of these 5, different experiments, really only 2 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 points, they're not really contributing to 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, curve levels off. And again it's leveling off here at this green region, and it's approaching the vmax at this green region. And so, because we have less data points, we only have 2 of the 5 total experimental data points helping us, contribute to where this v max value is. That's not all of the data points contributing. And so since there's less data points, that's why we get an inaccurate measure. And so, because the kilometers is associated with half of the v max and we're getting an inaccurate measure of the v max. That means that we're also gonna 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 a Michaelis Menten plot. However, now if we take a look at our Lineweaver Burk plot on the left, again, recall that a Lineweaver Burk 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 reciprocals, notice that our data is going to form a line of best fit. So when we plot our 5 experimental data points on this plot, we would have, five all be essentially falling onto the same line. And so all 5 of these experimental data points are helping to contribute to, this line of best fit, and this line of best fit is going to determine the x, the y intercept here, as well as the x intercept down here. And so, because the y intercept here is associated with the v max, what we can say is that we have all 5 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 2 data points contribute, we're having all 5 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 our v max value is going to be. So from plotting the same exact experimental data onto a Lineweaver Burk plot, we're able to get a more accurate measurement of the v max obtained from the, red point here. And also notice that the kilometers is going to be associated with the x intercept and all 5 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 Lineweaver Burk plot, we're 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 Lineweaver Burk plot will help us get a more accurate measurement of both the v max and the kilometers in comparison to a Michaelis Menten plot. And really, that's the main takeaway of this video, and we'll be able to apply the concepts that we've learned here in our practice problem. So I'll see you guys there.
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Problem
Problem
Why is it preferable to use a Lineweaver-Burk over a Michaelis-Menten plot when studying enzyme kinetics?
A
To directly visualize Km & Vmax on the plot.
B
To plot kinetic data as a hyperbolic curve instead of a line.
C
To obtain a more accurate measure of the V0.
D
To remove terms that cannot be calculated in a typical enzyme kinetics experiment.
E
To get more accurate estimates of Km & Vmax.
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Problem
Problem
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.