VARIATIONS ON A THEME BY DEBYE AND WALLER - FROM SIMPLE CRYSTALS TO PROTEINS

Debye and Waller showed how to adjust scattering intensities in diffra ction experiments for harmonic motions of atoms about an average, stat ic reference configuration, However, many motions, particularly in bio logical molecules as compared to simple crystals, are far from harmoni c. We show how, using a variety of simple anharmonic, multiconformatio nal models, it is possible to construct a variety of Generalized Debye -Waller Factors, and understand their meaning, A central result for th ese cases is that, in principle, intensity factors cannot be obtained from true total mean square displacements of the atoms, We make the di stinction between the intensity factors for unimodal quasiharmonic mot ions and those for the anharmonic, multimodal (valley hopping) motions . Only the former affect the conventional B factors. (C) 1997 Wiley-Li ss, Inc.dagger