It is difficult! Ni & Zn are rather interchangable.. You dont say what resolution you have: There will be a small difference in the number of electrons you expect to see at the metal site, depending on whether it is Zn Zn2+ etc etc, and you can correct that to take account of the f' as well. So you would expect a slightly smaller peak for Ni than Zn but it will be hard to give a definitive answer unless you have high resolution data.
First Q - was there Zn or Ni or both around in the crystallisation mix? Second Q: consider the coordination: This article discusses examples. Journal of Inorganic Biochemistry <http://www.sciencedirect.com/science/journal/01620134> Volume 71, Issues 3–4 <http://www.sciencedirect.com/science/journal/01620134/71/3>, September 1998, Pages 115–127 Eleanor On 1 July 2014 16:10, Dhanasekaran Varudharasu <dhana...@gmail.com> wrote: > 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 > > > >
