Scatchard equation

Scatchard plot is a possibility to check the enzyme activity cooperativity, that is to answer the question whether the enzyme by the binding of a first ligand having a higher or lower affinity for another ligand in addition to the Hill plot. ( The Eadie - Hofstee diagram represents the same with reversed axes dar. )

When the equation for the enzyme saturation

Transforms according to

One obtains the Auftragungsform for the Scatchard plot. Y here is the saturation and [L ] is the ligand concentration, K is the dissociation constant and Ymax for the maximum possible enzyme saturation. Concentrations are frequently measured in M = mol / L, with nM or uM are typical orders of magnitude.

Shape of the graph

Now gives an approximately linear plot, are on the y -axis and Y in Y / [L ] is set to the x-axis, wherein K 1 is the slope.

Information that can be read from the graph

• In the case of a non- allosteric enzyme ( the bond strength does not depend on the number of previously bonded substrate or ligand molecules from ) the graph shows a linear decrease.
• In the case of an allosteric, cooperative working enzyme gives a downward parabola open.
• In the case of negative cooperativity or non-identical, isolated binding sites results in a concave curve ( right curved, or second derivative - so existent - negative) with linear terminal branch.

The slopes here correspond to the affinities ( dissociation constant Kd of or the Michaelis constant Km).

• The total number of binding sites ( active sites ) can be read from the point of intersection with the x-axis.