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Home Q & A Board Biology-Related Homework Help Biochemistry
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torious torious
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7 years ago
Can someone provide reasoning to why x-int = -1/Km?
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Answer rejected by topic starter
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#1
Educator
7 years ago
This Lineweaver-Burk transformation converts the Michaelis-Menten curve into a straight line. Rather than plotting rate as a function of substrate concentration, their inverses were plotted as shown here.



You can see that the hyperbolic curve becomes a straight line. What is even more helpful is that the absolute value of the x-intercept of this line is the affinity (1/Km) of the enzyme for the substrate. The y-intercept is 1/Vmax (note the sign-error in the pdf file!). The slope of the line is Km/Vmax. Again, originally this was done subjectively. Later, computers permitted least-squares fit of linear models to data (linear regression); this statistical process removed the subjective component.

Today, people use either linear regressions on Lineweaver-Burk transformed data or they do non-linear regression of raw data to fit to the Michaelis-Menten function. In our laboratory exercise, we will use this much finer method for finding the best-fit parameters for the untransformed Michaelis-Menten relationship.
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torious Author
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#2
7 years ago Edited: 7 years ago, torious
That doesn't answer my question. From the lineweaver-burk plot, we know that
1/V = Km/Vmax * 1/S + 1/Vmax

If we set x = 1/S = 0 to get the y-intercept, we see that the y-intercept is equal to 1/Vmax.
1/V = y-int = Km/Vmax*(0) + 1/Vmax = 1/Vmax

How can we derive the x-intercept? Because I don't see how setting y = 1/V = 0 can give us x-int = -1/Km.
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#3
Educator
7 years ago
Can't you set y = 0 and solve for the root?
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torious Author
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#4
7 years ago
It doesn't give you -1/Km. I'm wondering how -1/Km was derived. If you don't know, then please don't clog up the response.
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bio_manbio_man
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7 years ago
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