Question

1. What is Y in terms of ligand binding? What is the definition of Kd? How are Y and Kd related? What is the meaning of affinity between a ligand and a protein? How is Kd related to affinity?

2. What do the binding curves of hemoglobin and myoglobin look like? Why are they different, what give hemoglobin’s curve a distinctive shape? How does a lower pH effect the hemoglobin binding curve?

Answer 1

The fractional saturation, Y, is defined as the ratio of macromolecule with ligand bound to the total amount of macromolecule

KD has units of molarity and is the ligand concentration when one-half of the macromolecules have ligand bound, i.e. [M]=[ML]

it is given b formula,

KD=[M][L ]/ [ML]

Binding affinity is the strength of the binding interaction between a single biomolecule (e.g. protein or DNA) to its ligand/binding partner (e.g. drug or inhibitor). Binding affinity is typically measured by the equilibrium dissociation constant (KD), which is used to find and rank order strengths of bimolecular interactions. The smaller the KD value, the greater the binding affinity of the ligand for its target.

binding curves are given in belo fig

myoglobin saturation curve is a rectangular hyperbola, NOT sigmoid. This different shape is the result of having a single subunit

sigmoid shape is a consequence of the four subunits of hemoglobin "cooperating" in the binding of oxygen.