Scatchard diagram

In addition to the Hill diagram, the Scatchard plot is a way of checking enzyme activity for cooperativity , i.e. answering the question of whether the enzyme has a higher or lower affinity for other ligands after binding a first ligand. (The Eadie-Hofstee diagram shows the same thing with the axes reversed.)

If you look at the equation for enzyme saturation

${\displaystyle Y={\frac {Y_{\text{max}}\cdot [L]}{[L]+K}}}$

reshaped after

${\displaystyle {\frac {Y}{[L]}}={\frac {Y_{\text{max}}}{K}}-{\frac {1}{K}}\cdot Y}$

the form for the Scatchard plot is obtained. Y is the saturation and [L] the ligand concentration , K stands for the dissociation constant and Y _max for the maximum possible enzyme saturation. Concentrations are often measured in M = mol / l , where nM or µM are typical orders of magnitude.

Some diagrams. The Scatchard chart is in the center right

Shape of the graph

An approximately linear plot is obtained with Y / [L] on the y-axis and Y on the x-axis, where -K ^{−1 is} the slope.

Information that can be read from the graph

• In the case of a non- allosteric enzyme (the strength of the bond does not depend on the number of substrate or ligand molecules already bound) the diagram shows a linear decrease.
• In the case of an allosteric, cooperatively working enzyme, a parabola that opens downwards is obtained.
• In the case of negative cooperativity or non-identical, isolated binding sites, a concave course (curved to the right, or second derivative - so existent - negative) with a linear terminal branch arises .

The slopes here correspond to the affinities (-K _d ⁻¹ or -K _a ).

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

See also

• Enzyme kinetics for other such diagrams

literature

• Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6 edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
• Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .