Sigmoid

The shape of a binding hyperbola when the data are plotted on a logarithmic concentration scale (logarithmic X-axis). The same information can be obtained from the sigmoidal curve as can be obtained from a hyperbola; the X-value at which the degree of binding is 50% of B_max is the log₁₀K_D value (or ln K_D, if a natural logarithmic scale was used). The lower plateau of the sigmoid is typically 0 and the upper plateau is B_max. In the presence of a competitive inhibitor or antagonist, the sigmoidal curve is shifted to the right.

An example of hyperbolic and sigmoidal binding curves is provided under the manual entry for hyperbola.