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 Bmax is the log10KD value (or ln KD, if a natural logarithmic scale was used). The lower plateau of the sigmoid is typically 0 and the upper plateau is Bmax. 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.