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tcheng888
#1 Posted : Wednesday, July 27, 2016 4:12:02 PM
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The EK book says that the Michaelis Constant does not change with the variation of enzyme concentration. How is this possible? Doesn't enzyme concentration directly influence the Vmax?
If I'm not mistaken, the chain of effect should look something as follows:
[Enzyme] -> Vmax -> Vmax/2 -> Michaelis Constant

Perhaps there's something in the Michaelis-Menten assumptions that I've missed?
Much appreciated
-Tony
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jamieward
#2 Posted : Wednesday, July 27, 2016 4:59:11 PM
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Hello Tony

You are correct in thinking that enzyme concentration will directly influence Vmax; the more enzyme you have, the more substrate that can be processed essentially.

Unfortunately, there is no good intuition for Km. You may have to just remember that Km is an inherent property of the enzyme and is independent of enzyme or substrate concentration. Km is derived mathematically from the rate constants of the forward and reverse reactions forming the enzyme-substrate complex. I have included a link of the derivation (way beyond the scope of the MCAT) mainly so you can see it is quite a bit more complicated than your (logical) reasoning above.

Key takeaways: Km is an inherent property of the enzyme (independent of enzyme or substrate concentration). A low Km means the enzyme has a high affinity for substrate and vice versa. Vmax is the maximal rate of a reaction and occurs when the enzyme is saturated.

Hope that helps!

http://imgur.com/rupRg8j
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