Practice question

Fractional saturation Y is defined as the concentration of ligand-bound receptor divided by the total receptor concentration, Y = [RL]/([R] + [RL]). Under equilibrium mass-action kinetics this expression simplifies to Y = [L]/(Kd + [L]). The equation predicts a hyperbolic binding isotherm whose midpoint occurs when free ligand concentration equals Kd, providing a direct experimental route to affinity determination.