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[Summary] - [ccp4bb]: Distinguishing betweem Mg+2 and water



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Dear all,

  Many thanks for all of the answers. 17 (!) in total (people are really 
inspired). On other hand, it will be a little difficult to write a “detailed” 
summary.
  In general lines, people suggested me to see coordination, the number of 
coordinators, the distances (but care with the refinement restraints) and the 
angles (also geometric figure implicit), either calculated by programs or 
looking through graphical ones. Normally oxygens coordinate Mg.
  Some cited the possibilitiy of substituting Mg, mainly by Mn (but also other 
metals), which indeed show up in the maps (either fourrier or anomalous). The 
labour could be justified by the necessity of confirming the sites.
  Some cited relevant articles. Also, some pointed to programs and websiste:
- WASP program; Nayal, M., & Di Cera, E. (1996) J. Mol. Biol. 256: 228-234. 
this will check if any waters could be Na+, Li+, Mg+2 or Ca+2
- try XPAND from X-UTIL http://xray.bmc.uu.se/gerard/usf/
- HIC-up (http://xray.bmc.uu.se/hicup/) for Mg with 1,2,3,4,5 and 6 waters 
coordinated.
  I will check all of them.
  Several cited that looking at B’s is tricky, specially at my resolution (2.2 
A). Anyhow, an experience related was: “the map showed the Mg peaks as I went 
in for higher sigma levels, the water balls in the map disappeared at higher 
sigma level”. Well, I do not know at 2.2, will check anyhow, but it must be an 
interesting procedure at higher resolutions.
  Many thanks for all of the suggestions and sorry for not giving personal 
credits on each one, as I received so many answers.
  P.S.: if someone is interested, I have a textfile with all of the complete 
answers. Ask me privately.

	Jorge