Dear Dhanasekaran, I am not sure from your email whether is important for you to resolve this ambiguity with crystallographic techniques. If not, an easy and simple way would be to shoot your crystals at energies above the Zn absorption edge (which is at highest energy of the two metals) and then collect a fluorescence spectrum. This can be done at most synchrotrons with tuneable beamlines and fluorescent detector. In fact even a fixed beam with standard energy at around 12 KeV will do for Zn and Ni.
Another possibility that springs to mind is inductively coupled plasma - atomic emission spectroscopy (or ICP-AES), usually available in chemistry departments. For this you don’t even need crystals, just a purified protein solution sample. HTH D From: Dhanasekaran Varudharasu [mailto:[email protected]] Sent: 01 July 2014 16:11 To: ccp4bb Subject: [ccp4bb] Metal ion differentiation - reg Dear all, I have solved a structure (using molecular replacement) of metallo-enzyme which may have Zn or Ni at its active site. I collected data at in-house CuKa radiation. Now, I am able to locate the active site metal ion preciously but I am not able to differentiate whether it is Zn or Ni. I computed anomalous difference map and I got good anomalous map also. But still there is ambiguity, since Zn and Ni have closest F" values at CuKa radiation ( For Zn = 0.68 and For Ni = 0.51). But both, Zn and Ni have different F' values at CuKa radiation ( For Zn = -1.61 and For Ni = -3.07). My question is that, Can we used F' value information to differentiate metal ions?. Is it possible to find whether I have Zn or Ni at active site of my enzyme using crystallographic technique?. Thanks in advance -- Dhanasekaran Varudharasu Post-Doctoral Fellow Department of Oral Biology Rutgers school of Dental Medicine Rutgers Biomedical and Health Sciences Newark, NJ 07103 USA
