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Weak/fast-off rate binding, slow isomerization

Here we will compare outcomes of the four alternative models for conditions when binding is weak and the off-rate is fast. The isomerization is chosen to be slow here. I choose binding affinity of 106 M-1 and the off-rate constant of 500 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 1 s-1 to make kex = 6 s-1 .

Location: Af_Bs/

Simulate setup U_Af

Simulate setup U_R_Af_Bs

Simulate setup U_L_Af_Bs

Simulate setup U_RL_Af_Bs

Both forward and reverse titrations look the same 2-site binding Very remarkable difference between the forward and reverse titration is expected in this case, easily detectable in spectra.

Both forward and reverse titrations will have the same signature of shifting disappearing peaks and the peaks appearing at fixed position, corresponding to more populated R*L.

IMPORTANT: This spectral appearance is very similar to U_R2 model! Reverse and direct titration in that case will be different !






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