On Tue, Jul 24, 2012 at 10:14 AM, Haytham Wahba <haytham_wa...@yahoo.com> wrote: > 1- if i have anomalous peak of unknown heavy atom, How can i identify this > heavy atom in general. (different methods) > > 2- in my case, i see anomalous peak in heavy atom binding site (without any > soaking). preliminary i did mass spec. i got Zn++ and Cu, How can i know > which one give the anomalous peak in my protein. > > 3- there is way to know if i have Cu+ or Cu++.
You may be able to identify the element based on the coordination geometry - I'm assuming (perhaps incorrectly) that it is actually different for Cu and Zn. Marjorie Harding has written extensively on the geometry of ion binding: http://tanna.bch.ed.ac.uk/ The only way to be certain crystallographically, if you have easy access to a synchrotron, is to collect data above and below the K edge of any candidate element, and compare the difference maps. (For monovalent ions it is more complicated, since they don't have accessible K edges.) On a home source, Cu should have a larger anomalous map peak, but I'm not sure if this will be enough to identify it conclusively. -Nat
