Back to Analysis of Direct and Reverse Titrations


Intermediate tight/-off rate binding, intermediate isomerization

 

Here we will compare outcomes of the four alternative models for conditions when binding is moderately tight and the off-rate is intermediate. The isomerization is chosen to be intermediate here. I choose binding affinity of 107 M-1 and the off-rate constant of 50 s-1. R and RL are separated by 100 s-1 and R* or R*L - by 100 s-1 from corresponding species. Isomerization equilibrium is shifted 5:1 toward *-forms. The reverse isomerization rate is 17 s-1 to make kex =100 s-1 .

Location:  Ai_Bi/

Simulate setup U_Ai

Simulate setup U_R_Ai_Bi

Simulate setup U_L_Ai_Bi

Simulate setup U_RL_Ai_Bi

 

 


The initial peak is going into slower exchange mode as the weighted average final peak shifts away. Therefore the initial peak shifts onto the position of pure R*.

Both direct and reverse titration with give the same result.  Direct and reverse titrations will produce markedly different behavior:  fast exchange for the non-isomerizing NMR-labeled component and shifting of the final and (to lower extent) initial peak Both forward and reverse titrations will exhibit shifting initial and immobile final peaks.

 

 

Back to Analysis of Direct and Reverse Titrations