functional functional target-based An assay where the measure signal is a direct or coupled readout of the proteins native mechanistic or conformational cycle. This can include: (1) assays that directly or indirectly measure product of an enzymatic cycle (e.g.: NADPH consumption, antibody based detection of phosphorylated peptide substrate, mass spec product detection and quantitation, electrofluidic mobility shift assay, etc); (2) assays that directly or indirectly measure the transmission of signal as a result of the interaction with a membrane bound receptor detected through fluorescent dye that detects the release of intracellular calcium, nuclear receptor, and (3) biochemical assays that measures the increase or decrease of an RNA transcript as a result of interaction with a nuclear receptor