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Match the dissociation constants in the table below to the appropriate curves on the graph.
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8. Protein Function
Protein-Ligand Fractional Saturation
Multiple Choice
Consider the following graph for parts A-C.
A) What is the protein-ligand dissociation constant (Kd) for protein X?
a) 2 µM. b) 4 µM. c) 6 µM. d) 8 µM.
B) What is the protein-ligand dissociation constant (Kd) for protein Y?
a) 2 µM. b) 4 µM. c) 6 µM. d) 8 µM.
C) Which protein has a greater affinity for ligand A?
a) Protein X. b) Protein Y.
A
2 µM.
B
4 µM.
C
6 μM.
D
8 μM.
Verified step by step guidance1
Identify the dissociation constant (Kd) from the graph, which is the ligand concentration at which the protein is 50% saturated. This corresponds to the point where the curve intersects the horizontal line at θ = 0.5.
For protein X, locate the point on the X-axis ([L]) where the black curve intersects the red dotted line at θ = 0.5. This concentration is the Kd for protein X.
For protein Y, locate the point on the X-axis ([L]) where the green curve intersects the red dotted line at θ = 0.5. This concentration is the Kd for protein Y.
Compare the Kd values for proteins X and Y. The protein with the lower Kd value has a greater affinity for the ligand, as it reaches 50% saturation at a lower ligand concentration.
Use the identified Kd values to answer the questions: A) Kd for protein X, B) Kd for protein Y, and C) which protein has a greater affinity for ligand A.
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