Figure 3.

Newman plot of tryptophan χ^2,1 dihedral angles for proteinaceous tryptophans (triangles) and model peptides (crosses), as given in Table 1, and for crystalline tryptophan derivatives (diamonds) from (2). The three allowed (stars) tryptophan dihedral angles for an α helix, as determined from a dataset of 61 globular proteins in the Protein Data Bank, are also plotted (29). All negative dihedral angles are plotted as χ^2,1_360° = 360° + χ^2,1. Concentric with the plot is a Newman diagram showing the disposition of the tryptophan indole C₂==C₃ bond with respect to the C_β ---C_α bond along the C_α–C_β–C₃=C₂ linkage.