Lab of Vmax and KM

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Lab of Vmax and KM

Post by NewtoBiology » Thu Jul 09, 2009 5:34 am

Hello Biologists,

I conducted a lab today at school about the effect of substrate concentration on amylase activity.
I recorded 28 points with [S] (mM) and V (mM/min).
I subsequently plotted two graphs (a Michaelis-Menten and Lineweaver burk) and calculated the Vmax and Km.

Vmax = 0.005033 mM/min
KM = 23.41

So that I completely understand: the maximum velocity this enzyme can react at is 0.005022 mM/min at which time it will be totally saturated. Meaning it will not react ANY FASTER..... Is this correct?

My question is this: (it is not a homework question, because I always answer my own questions to the best of my abilities before posting... this is just for my own understanding) what would happen if I carried out the experiment again at school tomorrow with a starch concentration greater than 400 nM.

FYI: my last three plots were 360 mM - 0.00487 mM/min
380 mM - 0.00477 mM/min
400 mM - 0.00473 mM/min

Here's what I think... but I AM SO NEW TO THIS biochemistry stuff, so knowing me I'd blow the whole place up...

Knowing that the Vmax is 0.005033 mM/min I know that shortly after a concentration of 400 mM the enzyme will be saturated. Therefore is it safe to answer my own question by saying that if I started another experiment with concentrations greater than 400 mM the Vmax would quickly be met, and the rest of my graph (or velocity) would plateau, and not go any faster, while my substrate concentration continued to get larger?

Thank you for your patience biologists, I am so grateful for you time and help!!

New to biology.

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Re: Lab of Vmax and KM

Post by jonmoulton » Thu Jul 09, 2009 4:00 pm

That's it. The velocity approaches Vmax asymptotically as the substrate concentration increases. However, changing other conditions can change the Michaelis–Menten plot -- for instance, a different pH or a different temperature can lead to a different relationship between [S] and Vmax.

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