Q.45 Scatchard analysis of ligand-receptor interaction yielded the graph shown below.
The affinity of the ligand-receptor interaction can be obtained from
Bound / Free
Bound (molar)
Correct Answer
Option (C): Slope of the line
Concept of Scatchard Analysis
Scatchard analysis is a graphical method used to study ligand–receptor
binding interactions and to determine binding affinity and total binding sites.
The Scatchard equation is:
Bound / Free = (Bmax − Bound) / Kd
In a Scatchard plot:
- X-axis: Bound (molar)
- Y-axis: Bound / Free
Parameters Obtained from the Scatchard Plot
- Slope = −1 / Kd → Indicates affinity
- X-intercept = Bmax → Total binding sites
- Y-intercept = Bmax / Kd
Why Affinity Is Obtained from the Slope
Affinity is inversely proportional to the dissociation constant
Kd. Since the slope of the Scatchard plot equals
−1 / Kd, the slope directly represents
ligand–receptor affinity.
A steeper negative slope indicates higher affinity, while a flatter slope
indicates lower affinity.
Exam Tip
In Scatchard analysis, ligand–receptor affinity is always obtained from the slope of the graph.
