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Fast exchange between the two peaks:
Side-by-side comparison and how to discern the mechanisms

Location: tutorial_simulations/Spectral_patterns/2/

Calculations from tutorial_spectral_patterns_2.htm

Now we will put these models side-by-side as if performing a series of experiments

 

 

 

Model
Populations graph
ITC profile
Dependence of the position of the unbound receptor peak upon 20x dilution
Dependence of the position of the final saturated (L/R=2.5) receptor peak upon 20x dilution
Forward titration
Chemical shift change upon titration
Line broadening
Fit with U model
  
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  • Fitted Ka =1/Kd = 1.7e+06 M-1 is in a good agreement with the pre-set Ka=1e6.
  • Fitted Koff =1080 s-1 agrees well with the preset k2=1000 s-1.

 
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 Note a remarkable discrepancy between the 2-site U-model and U_R data due to the mismatch of the line-broadening effect across the L/R range.
Titration curve is not accurate as heat effects of a titrant are not considered in this LineShapeKin Simulation version.
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Ka=1/Kd= 0.67e+06 versus Ka=1e6 used in the simulation. Ka is supposed to be  scaled down by the competing formation of L*.

Koff is accurate: 1040+-30/s vs. 1000/s used in the simulation.
Dramatic discrepancy between the U model fit and U_R2 data originates from the non-linear peak shifts in the beginning of titration.
Titration curve is not accurate as heat effects of a titrant are not considered in this LineShapeKin Simulation version.
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Ka=1/Kd = 0.37e6  vs. 1e6 used for simulation

Koff=1090 /s - close to 1000/s used.
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The fit is relatively good, with a slight mismatch due to line width differences.

Remarkable that Ka=1/Kd= 7e+06, which is 7x larger than 1e6 used in the simulation.

In opposite, Koff=150/s, much slower than the k2(A)=1000/s and k2(B)=1000/s used in the simulation.
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