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# Protein-Ligand Fractional Saturation

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Sections
Introduction to Protein-Ligand Interactions
Protein-Ligand Equilibrium Constants
Protein-Ligand Fractional Saturation
Myoglobin vs. Hemoglobin
Heme Prosthetic Group
Hemoglobin Cooperativity
Hill Equation
Hill Plot
Hemoglobin Binding in Tissues & Lungs
Hemoglobin Carbonation & Protonation
Bohr Effect
BPG Regulation of Hemoglobin
Fetal Hemoglobin
Sickle Cell Anemia
Chymotrypsin
Chymotrypsin's Catalytic Mechanism
Glycogen Phosphorylase
Liver vs Muscle Glycogen Phosphorylase
Antibody
ELISA
Motor Proteins
Skeletal Muscle Anatomy
Skeletal Muscle Contraction

Concept #1: Protein-Ligand Fractional Saturation

Concept #2: Max Theta

Concept #3: Max Theta

Example #1: If an antibody binds to an antigen (ligand) with a Kd of 5 x 10-8 M, what concentration of antigen will θ = 0.2?

Practice: 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.

Practice: Match the dissociation constants in the table below to the appropriate curves on the graph.

Practice: Use the table below to answer questions A, B & C below.

A) Which protein has a greater affinity for their ligand?

B) According to the data in the table, what is the dissociation constant (Kd) for Protein 1?

Protein 1 Kd = ________

C. According to the data in the table, what is the association constant (K a) for Protein 2?

Protein 2 Ka = ________

Practice: A sample of cells has a total protein-receptor concentration of 10 mM. 25% of the protein-receptors are occupied with ligand when the concentration of free ligand is 15 mM. Calculate the Kd for the receptor-ligand interaction.