Figure 4. Binding affinity of the ligand peptides to CRIP1 from saturation binding (apparent K _d) and from competitive binding (IC₅₀).

(A) The apparent K _d for binding of FITC-A1M to CRIP1 protein was determined by a saturation binding experiment using 1 mM of unlabeled A1M peptide to assess non-specific binding, K_{d apparent}  =  2.6 uM. Error bars represent the S.E. of the corrected mean. (B) To compare the binding affinity of A1M and A1 to CRIP1 we performed a competitive binding assay. The concentration of the labeled ligand (FITC-A1M) was held constant and increasing concentrations of either unlabeled A1M or unlabeled A1 peptides were used to compete the binding. From these binding curves regression analysis was used to calculate the IC₅₀ for each of the competitors. Both peptides competed off FITC-A1M suggesting that there is only a single binding site for this peptide on the CRIP1. A1M was approximately 27.5 times more effective than A1 at competing for FITC-A1M binding to CRIP1. Error bars represent S.E. of the corrected mean.