You study ligand binding to two proteins, A and B. You measured the concentratio

Question

You study ligand binding to two proteins, A and B. You measured the concentration, [PL], of the ligand-bound form of the protein at various ligand concentrations, [L_t]. The data are summarized in the two tables below. Note that you do not know the total concentration of the protein, but you know that adding more ligand did not noticeably change the bound-protein concentration. Based on these data, answer the following questions: Determine the [P_t] and K_d values for each of the proteins. Explain your assumptions. Which of the two proteins binds the ligand tighter? Explain your reasoning. Is this binding cooperative or non-cooperative? Prove it?

Explanation / Answer

1. Kd is the equilibrium binding constant, It is the ligand concentration needed to achieve a half-maximum binding at equilibrium. For this, you need to plot the graph and determine the maximal binding for each protein.

Protein A Bmax= 0.22uM, Kd= 70uM

Protein B Bmax= 0.8uM, Kd= 100uM

2. Higher Kd, indicates lower affinity and lower Kd indicates higher affinity.

So protein A binds ligand tighter than protein B.

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