Unexpected peaks in a S-SAD experiment sometimes turn out to be chloride, sulfate or a metal ion. I would suggest that you run shelxd with and without the disulfide option (or with different numbers of disulfides) to see which is best, and also run SHELXE with the -b flag set. This will produce an analysis of the anomalous density at the sites that you inputted and a list of peaks in the anomalous map. I also suggest that you look at the anomalous density by feeding the .pha file from SHELXE (generated if -b is set) into e.g. Coot.
George Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-22582 On Thu, 25 Sep 2008, Michael Jackson wrote: > Hello, > I had recently collected and solved the phases for a protein molecule using > CCP4 and the ShelXCDE SAD method in it. What I was wondering was that the > peaks for the three SE incorporated methionines are there as expected, but > there is one peak scored roughly as the second largest where the disulfide is > based on ShelXD's HA search algorithm. This data was collected at 0.97960 > Angstroms which is close to the peak Xray absorption edge for Se but does > anyone know if a disulfide has any absorption edge overlapping here? > > > >
