1. Relationship between Affinity and Dissociation Constant Protein A has a bindi
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Question
1. Relationship between Affinity and Dissociation Constant Protein A has a binding site for ligand X with a Kd of 10-6 M. Protein B has a binding site for ligand X with a K of 10-9 M. Which protein has a higher affinity for ligand X? Explain your reasoning. Convert the Kd to Ka for both proteins 3. Hemoglobin's Affinity for Oxygen What is the effect of the following changes on the Op affmnity of hemoglobin? (a) A drop in the pH of blood plasma from 7.4 to 7.2. (b) A decrease in the partial pres- sure of CO2 in the lungs from 6 kPa (holding one's breath) to 2 kPa (normal). (c) An increase in the BIG level from 5 mM (normal altitudes) to 8 mM (high altitudes). (4) An increase in CO from 1.0 parts per million (ppm) in a normal indoor atmosphere to 30 ppm in a home that has a malfunctioning or leaking furnace. 4. Reversible Ligand Binding I The protein calcineurin binds to the protein calmodulin with an associa- tion rate of 8.9 × 10" M-1s-1 and an overall dissociation constant, Kd, of 10 ns. Calculate the dissocia- tion rate, kd, including appropriate units.Explanation / Answer
Affinity is the strength of binding of a single molecule to its ligand. It is typically measured and reported by the equilibrium dissociation constant (KD), which is used to evaluate and rank order strengths of bimolecular interactions. The binding of an antibody to its antigen is a reversible process, and the rate of the binding reaction is proportional to the concentrations of the reactants.
At equilibrium, the rate of [antibody] [antigen] complex formation is equal to the rate of dissociation into its components [antibody] + [antigen]. The measurement of the reaction rate constants can be used to define an equilibrium or affinity constant (1/KD). In short, the smaller the KD value the greater the affinity of the antibody for its target.
Protein B shows higher affinity due lower KD .
Since Ka is 1/KD , so Ka for Protien A = 106 and for Protien B = 109
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