Two proteins bind to the same ligand, and protein A has half of its binding sites occupied when the ligand concentration is 0.5 mM, while protein B has half of its binding sites occupied when the ligand concentration is at 0.3 mM. Which protein binds the ligand more strongly, and what is the dissociation constant for that protein-ligand interaction? A) Protein A binds more strongly, and K_d = 0.3 mM. B) Protein A binds more strongly, and K_d = 0.5 mM. C) Protein B binds more strongly, and K_d = 0.3 mM. D) Protein B binds more strongly, and K_d = 0.5 mM. E) Both proteins bind the ligand with the same affinity, and K_d = 0.4 mM.

Question

Quizplus · Accepted Answer

Protein B binds the ligand more strongly because it reaches half saturation at a lower ligand concentration (0.3 mM) compared to protein A (0.5 mM). The dissociation constant for protein B is given by the concentration of ligand at which half saturation is achieved, which is 0.3 mM. Therefore, the answer is C) Protein B binds more strongly, and K_d = 0.3 mM.

Two Proteins Bind to the Same Ligand, and Protein a Has