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Topic: Michaelis Menten and Enzyme Kinetics  (Read 3881 times)

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Offline limonade

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Michaelis Menten and Enzyme Kinetics
« on: May 08, 2016, 03:51:24 PM »
Hi
I would like to know if I am approaching the following problem correctly.  In particular, I would like to verfy that my assumption KM = Keq is correct for calculating gibbs free energy. Also , what is considered a "large" Kd value vs a small one for determining if an enzyme substrate complex is in its dissociated or associated form at equilibrium? Since Kd=1/Keq, would I just use Kd = 1/Km?

Thank you

Offline limonade

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Re: Michaelis Menten and Enzyme Kinetics
« Reply #1 on: May 08, 2016, 11:30:55 PM »
whoops. I think I made a mistake. the problem says k2<<k-1

sooo I think I should have my Km= Kd
then just take the point where Km= 1/2 Vmax = 1/2 *9.6 from the table I suppose. If anyone can confirm I would appreciate it :)

Offline mjc123

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Re: Michaelis Menten and Enzyme Kinetics
« Reply #2 on: May 09, 2016, 05:07:57 AM »
I'm not a biochemist, but there are some obvious problems here.
There are not one but three equilibrium constants here (two independent); one for each of the separate equilibria and one for the overall reaction:
K1 = [ES]/[E][S ]; K2 = [E][P]/[ES]; Keq = [P]/[S ] = K1K2
You are asked for ΔG° for the first step, not the overall reaction, so you need -RTlnK1, not -RTlnKeq.
The statement KM = Keq for k2>>k-1 is wrong; KM and Keq have different units.
For k2<<k-1, KM = k-1/k1 = 1/K1
so ΔG° = -RTln(1/KM)

Offline Babcock_Hall

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Re: Michaelis Menten and Enzyme Kinetics
« Reply #3 on: May 09, 2016, 08:57:54 AM »
When I work with a Lineweaver Burk plot, I find 1/Vmax from the y-intercept of the graph.  Then I calculate KM using the slope of the L-B plot and the value of Vmax.  The Al Gebra is quite easy.  Just don't do it on an American Airlines flight.
EDT
KM is approximately equal to Kd under the conditions that the problem specified.  But Kd is the dissociation constant of the substrate from the enzyme, not the equilibrium constant.  The relationships between the kinetic constants and the equilibrium constant for the reaction are called the Haldane relationships, after JBS Haldane.

Offline limonade

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Re: Michaelis Menten and Enzyme Kinetics
« Reply #4 on: May 09, 2016, 10:29:48 AM »
Thanks to all for your help

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