The part of a dose-response curve where the Target is in the bound state is also called saturation. The opposite, the unbound state, is also called Baseline.

Generally, saturation describes a situation where all binding sites of a molecule are occupied, and further addition of a binding partner will (and can) not cause the occupation of any more binding sites.

In DI.Screening Analysis, the saturation of a dose-response curve is also computed and returned to the user as a % value. This saturation level is computed from the fitted dose-response curve in the following way:

When a flat dose-response is obtained, one can differentiate between a non-binder ligand from a saturated at the lowest concentrations by comparing the values of the reference points (i.e DMSO) to the assay points. If the lower concentrations of the ligand are significantly different from the reference, the interaction is already saturated and the interaction needs to be tested at lower ligand doses. But, if the values between the reference and the highest concentrations of the assay points are similar, the compound is not a binder under those conditions.

The absolute value of the 670/650 ratio of a labeled target can vary depending on the Degree of labeling, the target concentration, the buffer, and the percentage of unfolded/aggregated target in the sample.