E. Weckert et al., DIRECT PHASING OF MACROMOLECULAR STRUCTURES BY 3-BEAM DIFFRACTION, Proceedings - Royal Society. Mathematical and physical sciences, 442(1914), 1993, pp. 33-46
Determination of triplet phases of macromolecular structures by means
of psi-scan experiments are reported. The ways in which difficulties c
an be overcome when investigating macromolecular structures (numerous
overlap of multiple beam diffraction profiles, overall weak scattering
power and radiation damage) are discussed. It is shown theoretically
and experimentally that measurable interference effects exist if the c
rystal dimensions are smaller than the Pendellosung length. The effect
of the unavoidable overlapping of weak three-beam cases is negligible
if a three-beam case with strong reflections is selected for phase de
termination. Data recorded at the HASYLAB synchrotron radiation source
DORIS III are presented. In case of lysozyme it was possible to measu
re a set of 80 triplet invariants with a mean phase error of about 17-
degrees. First experiments to study the feasibility of phase determina
tion of large proteins, e.g. of catalase (unit cell volume 1200 nm3),
are presented.