Ligand Binding and the Scatchard Plot

Key points

1. 01

   $K_a = 1/K_d$: a high $K_d$ means low binding affinity; a high $K_a$ means high binding affinity.

2. 02

   The Scatchard plot linearizes saturation binding data: plot $r/[L]$ (or $\Theta/[L]$) against $r$ (or $\Theta$) to read off affinity and binding-site count without curve-fitting.

3. 03

   Slope $= -K_a$, y-intercept $= nK_a$, x-intercept $= n$.

4. 04

   $\Theta = r/n$ is fractional saturation, always between 0 and 1; $r$ itself is not bounded by 1 for a multi-site protein.

5. 05

   For a protein with a single binding site per molecule ($n = 1$), total binding-site concentration equals total protein concentration.