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Dear Dhanasekaran Varudharasu, you won't be able to distinguish between these two metals with CuKa radiation. You should get access to a synchrotron and collect data 1.4A and 1.25A in addition to the CuKa set you already have (see http://skuld.bmsc.washington.edu/scatter/AS_form.html). The CuKa data set with no (significant) anomalous peak is your control. If there is an anomalous peak at the 1.25A data set but not at 1.4, then it should be Ni, if both data sets contain peaks, it should be Cu - provided of course you can definitely rule out any other metal. If you are sure about this, you might as well to a fluorescence scan for which of course you don't need a crystal. Best, Tim On Tue, Jul 01, 2014 at 11:10:52AM -0400, Dhanasekaran Varudharasu 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 -- -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A