There is always an anomalous signal to be seen if one measures things well enough. One does not need to be at the edge in order to detect anomalous scatterers. For example, most (if not all) of the sulfur SAD phasing is done well away from the sulfur edge. I will note that you stated that the f' and f" of Fe at this wavelength was not zero, thus there should be a signal and a peak.
When you phase your data, you will get better phases if you describe ALL the anomalous scatterers and signals that are detectable and not just the Tb. Jim _____ From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Huiming Li Sent: Tuesday, August 09, 2011 11:38 AM To: [email protected] Subject: [ccp4bb] anomalous scatterer Hi All, I am working on a Tb binding protein on which I collected anomalous data at Tb edge of 1.648 A. Each protein is designed to bind one Tb. There are two copies of the protein in an ASU. I have two questions. First, I am only able to see one copy of the protein with Tb bound, and no density on the other copy. Isn't this a bit surprising? Second, there is one additional peak on each monomer at the site where Fe is known to bind, and Fe has an edge of 1.739A. At 1.648A, f' and f'' of Fe is only about 1/5 of Tb. Is it possible Fe also shows some anomalous signal at Tb edge? Thank you, Huiming Li, Ph.D. Immune Disease Institute Children's Hospital Boston Harvard Medical School Boston, MA 02115
