Fig. 5.

Plots ofI_NN/I_αN(small black dots and solid line) and pH titration (large gray dots and dotted line) data versus IC₅₀ measurements. The vertical axis is parts per million for the pH titration and unitless forI_NN/I_αN. The IC₅₀ data represent the concentration of peptide needed to displace 50% of ¹²⁵I-daYFnLRF-NH₂ from aHelix brain membrane preparation (Payza, 1987; Payza et al., 1989). TheI_NN/I_αNand pH titration data are from Table 1 and are described in the text. Data were fit to linear equations, IC₅₀ =a (NMR) + b(I_NN/I_αNdata: a = 33.33, b = −0.27,r² = 0.93; pH data:a = 41.67, b = −1.79,r² = 0.82). A data point for the pH dependence of pQYPFLRF-NH₂ at 0 ppm was added, because there is no titratable group and thus no pH dependence.