Scatchard equation

The Scatchard equation is an equation for calculating the affinity constant of a ligand with a protein. The Scatchard equation is given by

:$frac\{r\}\{c\}\; =\; nK\_a\; -\; rK\_a$

where r is the ratio of the concentration of bound ligand to total available binding sites, c is the concentration of free ligand, and n is the number of binding sites per antibody molecule.

K_a is the association (affinity) constant from the equation

:$K\_a\; =\; frac\{\; [Ab-Ag]\; \}\{\; [Ab]\; [Ag]\; \}$

where Ab is the binding site on the antibody, Ag is a monovalent antigen, and Ag-Ab is antigen-bound antibody.

The Scatchard equation is sometimes referred to as the Rosenthal-Scatchard equation.

Plotting this data, r/c vs r, yields the Scatchard plot with a slope -K_a and an X-intercept of nK_a. Relative binding affinities between two sites can be distinguished with a line showing identical affinity and a curve showing different affinities.

The Scatchard equation is named after the former MIT Chemistry Department member George Scatchard, an American chemist, 1892–1973.

See

* [http://www.graphpad.com/curvefit/scatchard_plots.htm some explanation]
* [http://www.unmc.edu/Pharmacology/receptortutorial/saturation/rosenthal.htm explanation]
* [http://www.unmc.edu/Pharmacology/receptortutorial/derivations/derivation_rosenthal.htm derivation]