Hello, Thanks for this interesting poll! I have had similar doubt couple of times in the recent past. I think in the absence of anomalous signal for confirming presence of phosphate or sulphate, I would prefer to assign the electron density to the one which is present in higher concentration in the crystallization drop. Just on the basis of electron density, co-ordination geometry and functional groups attached to the tetrahedral density, I assume it is very difficult to say if it is phosphate or sulphate.
In your case, I would go for SO4 instead of PO4. I would also like to know other people's experiences in such cases. Regards Simanshu On Sat, Apr 10, 2010 at 10:49 AM, wtempel <wtem...@gmail.com> wrote: > 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. > > -- Dhirendra K Simanshu Research Scholar Memorial Sloan-Kettering Cancer Center New York, NY, USA
