SAD phasing with triiodide, softer X-rays and some help from radiation damage.
SAD data on a triiodide derivative of porcine pancreatic elastase have been recorded from a single sample using 2.0 A wavelength X-rays. The large anomalous signal of iodine at this wavelength allowed the detection of heavy-atom sites and subsequent structure determination using low-redundancy data. Substantial radiation damage was observed during the measurements and this prevented the merging together of all data. However, a straightforward treatment of the radiation effects on the heavy-atom model during parameter refinement resulted in additional phase information being gleaned from the observed reduction in iodine occupancy factors, which in turn produced a significant improvement in the quality of the electron-density map.
Evans
Gwyndaf
G
Global Phasing Ltd, Cambridge CB3 0AX, England.
Polentarutti
Maurizio
M
Djinovic Carugo
Kristina
K
Bricogne
Gérard
G
D000818:Animals; D018360:Crystallography, X-Ray / Q000379:methods*; D004583:Electrons; D007454:Iodides / Q000737:chemistry*; D007455:Iodine / Q000737:chemistry; D008958:Models, Molecular; D010196:Pancreatic Elastase / Q000737:chemistry; D012984:Software; D013552:Swine; D014965:X-Rays
D007454:Iodides; D007455:Iodine; D010196:Pancreatic Elastase