Dear all. Thanks to all of those who replied to my question, especially Clemens Vonrhein, who patiently helped me get SHARP up and running...
Basically, there were 4 different ways suggested, with a few embellishments here and there. 1) Use Dano peak height. Taking the Dano peak height for intrinsic sulphurs as a standard, you can then estimate the f" of the unknown anomalous scatterer, and use that to discriminate between Ca & Mn. (In my case, Dano map was noisy below 4sig and only 2 out of 5 sulphurs had any sort of peak). (Jochen Kuper, Kay Diederichs, Remy Loris, Eleanor) One caveat is that the height of the Dano peak height is very B-factor dependant - one suggested solution was to use mapman to integrate a box/sphere around the anomalous scatterers (S and unknown) and calculate a ration of the peak height that way, which apparently tends to remove much of the B-factor dependence of the analysis (Stephen Graham, Mitch Miller) 2) Use a heavy atom refinment program, such as SHARP or Phenix xtal.refine to refine f" and/or f' values - inputting current phase probs as HLs. (Clemens & Peter Zwart) 3) Use Inductively coupled plasma optical emission spectroscopy (ICP-OES) to do an elemental analysis - Mn or Ca should be very obvious (Artem & Roger S. Rowlett) 4) atomic absorption spectroscopy (Charlie Bond) Other suggestions included trying to crystallise the protein in either Mn or Ca to see if it preferentially crystallises in one or the other. Other ideas suggested closer to home include (micro)PIXE, and intact mass analysis - maybe. The obvious scan around the Mn K edge is still the definitive crystallography-based test.. Thank you very much for all your helpful suggestions. Dave -- --------------------------------------- David Briggs, PhD. Father & Crystallographer www.dbriggs.talktalk.net iChat AIM ID: DBassophile --------------------------------------- Anyone who is capable of getting themselves made President should on no account be allowed to do the job. - Douglas Adams
