Competition was measured by the fluorescence anisotropy assay and with N(13-391) binding to P by SPR. Competitor peptide concentrations ranged from 0.2 to 200 μM. The IC50 for D(pS)DNDL(pS)LEDF was measured twice using fluorescence anisotropy. IC50s from the fluorescence anisotropy assay are approximately twice the Kds of the competitors because the N(13-391) concentration was set at the Kd for the interaction of N(13-391) with BP5. ND, not done.