Solid and dashed curves represent fluorescence-detected melting of the dimeric D-D fragment at 0.16 μM and the D-D:E1 complex at 0.12 μM, respectively. Melting of 0.16 μM D-D in the presence of a 100-fold molar excess of Gly-Pro-Arg-Pro or Gly-Pro-Arg-Pro and Gly-His-Arg-Pro are shown by open and filled circles, respectively, while that in the presence of a 1000-fold excess of Gly-Pro-Arg-Pro is shown by open triangles. All experiments were performed in 50 mM glycine buffer, pH 8.6, with 0.5 mM Ca2+.