Figure 3.

CD spectra of isolated peptides and the A_a, A_b, and B peptides in combination. (Upper) CD spectra of the individual A_a (filled circles), A_b (diamonds), and B (open circles) peptides; only the A_b peptide shows any appreciable helicity. (Lower) CD spectra of a 1:1:2 mixture of the A_a, A_b, and B peptides in the absence of divalent metal ions (filled circles) and in the presence of 50 μM zinc acetate (filled triangles). For comparison, the CD spectra calculated by summation of the spectra of the individual peptides are also shown for a 1:1:2 mixture of A_a, A_b, and B in the absence of metal ions (open circles) and in the presence of 50 μM zinc acetate (open triangles). In all experiments, the buffer was 10 mM 4-morpholinepropanesulfonic acid, pH 7.0/100 mM NaCl; the total concentration of peptide(s) was 30 μM.