FIG. 7.

Effects of stereochemistry on peptide binding. A d-amino acid (A) or glycine (B) was used as a substitution at various positions of peptide chains containing alanine or leucine, respectively. The abilities of the different peptides to compete with A1-10, A2-8, and A3-3 for binding to OppA-1, OppA-2, and OppA-3, respectively, were tested. Assays for OppA-1 and OppA-3 were performed at pH 7.0; assays for OppA-2 were performed at pH 5.0. Peptides were studied at a concentration of 20 μM. Experiments were performed a minimum of three times in duplicate; error bars represent standard errors of the means. dA, d-alanine; A, l-alanine.