Statistically derived Phi-psi maps for each type of residue indicate substantial improvements in X-ray data over previous tabulations. Position effects in regular secondary regions show strong effects for some types of residues, especially proline, aromatic and polar groups. A simple dipolar solvent model indicates an asymmetry to electrostatic interactions. Favorable interactions appear to be enhanced and extended to longer range. NMR investigations of an ACTH fragment indicated no dominant conformations. As with most small peptides, it was highly flexible.
