Inhibition of N(13-391) binding to immobilized P protein by D(pS)DNDL(pS)LEDF peptide measured by SPR. Concentrations of the peptide are indicated on the figure. The IC50 (curve shown in inset) was 13.7 ± 0.3 μM (best-fit value ± standard error of the best-fit value). The concentration of N(13-391) was 100 nM. Injection spikes have been deleted from the image for clarity.