ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The synchrotron X-ray beam produced by the SPEAR storage ring at the Stanford Linear Accelerator Center has been used as a tuneable and intense source for single-crystal-protein diffraction experiments. A measurement of the absolute intensity of a focused, monochromatized X-ray beam gave a value of 3 × 109 photons s-1 at a wavelength of 1.74 Å for typical machine operating conditions. A series of hk0 precession photographs were obtained from a crystal of the Fe-containing protein rubredoxin to investigate anomalous scattering effects and study their use in phase determination. Seven discrete wavelengths of radiation were used, some above and some below the Fe K absorption edge (1.743 Å = 7.111 keV). The rubredoxin diffraction data showed intensity changes due to f' varying with wavelength as well as from Bijvoet differences. The Fe site could be correctly located from difference Patterson and Fourier maps based either on f' or f”. The signal to noise ratio at the iron site was enhanced by calculating combined f' and f” maps. The phases of the Bragg reflections were also obtained from three films collected at different wavelengths. When compared with the known phases for rubredoxin, the differences average to 60°, which indicates that some phasing information was available even from the relatively poor data and that this method will be potentially useful in future applications. A method for calculating the Lp factor which has to be applied to precession photographs taken with the polarized synchrotron X-ray beam is described in the Appendix.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739477001168
