One might also check the pH of your crystal and the number of hydrogen bond donors from the putative sulfate (zero?) or the putative phosphate (non-zero). I'm alluding to the structures of the sulfate-binding protein and the phosphate-binding protein from Quiocho's group. Jim
_____ From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of wtempel Sent: Saturday, April 10, 2010 9:49 AM To: [email protected] Subject: [ccp4bb] phosphate v sulfate Dear colleagues, I would like to poll the community on the prevailing practice of distinguishing between phosphate and sulfate in their structures. Suppose all of the following apply: 1) a well contoured tetrahedral density in your model-phased 2Fo-Fc map in the active site of your kinase or GTPase protein. 2) a significant, say 5*sigma, coincident peak in your model-phased anomalous difference fourier map from data collected at a Cu rotating anode source. 3) The crystal grew in 2M ammonium sulfate. Please post your answers to the list if you feel this question is of general interest.* Thank you for your input. Wolfram Tempel *If it is not, I apologize to everyone for wasting their valuable time.
