Where in refinement of your model are you ? At an early stage I wouldn't be surprised to only see SeMets but once you've refined your structure and go back to calculate an anomalous map with the improved phases you might double your signal for SeMet and start seeing sulfurs. An alternative explanation, you've blasted your crystals at the synchrotron and the remaining anomalous signal is too weak to show the sulfurs.
Just two thoughts, Jürgen On Sep 1, 2011, at 4:03 PM, Jacob Keller wrote: Dear Crystallographers, I recently have been working with a 2.5 Ang SeMet peak wavelength dataset which contains 2 cys's and also a couple of bona fide Cl ions (reasonable b-factor/site is semi-buried/water does not work). In the FFT anomalous difference map using PhiC from the refined model and Dano, I can see the MSE's at ~10 sigma, but no Cl ions, even though Cl should have f" = ~0.3 versus Se's f" = ~4, and no S's in the cys, despite f" = 0.23e. There is really no anomalous peak at all--is it just the smallness of the signal, or are the Se's somehow "swamping out" the other signal? Perhaps the phases are tainted by the presence of semet in the model? Looking for suggestions, Jacob Keller ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program cel: 773.608.9185 email: j-kell...@northwestern.edu<mailto:j-kell...@northwestern.edu> ******************************************* ...................... Jürgen Bosch Johns Hopkins University Bloomberg School of Public Health Department of Biochemistry & Molecular Biology Johns Hopkins Malaria Research Institute 615 North Wolfe Street, W8708 Baltimore, MD 21205 Office: +1-410-614-4742 Lab: +1-410-614-4894 Fax: +1-410-955-2926 http://web.mac.com/bosch_lab/
