Fig. 2. (A) Binding isotherm of Fc-III-FAM to trastuzumab measured by fluorescence anisotropy. The trastuzumab concentration is gradually increased while the concentration of the Fc-III-FAM labeled peptide was kept constant (5 nM). The fluorescence polarization signal of the trastuzumab/peptide bound complexes is reported on the y axis. The black solid line corresponds to the fit of the data using the Hill equation, yielding the half-maximal effective concentration (EC₅₀). (B) Competition assays of Fc-III and PEG₂₀-Fc-III for trastuzumab against Fc-III-FAM. Black solid (Fc-III) and red dashed lines (PEG₂₀-Fc-III) are fittings of the data using the Hill equation yielding the half-maximal inhibitory concentration (IC₅₀).