[phenixbb] Off topic: Anomalous signal

Soisson, Stephen M stephen_soisson at merck.com
Wed Nov 14 12:02:48 PST 2012

Make sure that you have consistent indexing if you collected separate data sets at multiple wavelengths.  You can also experiment with local scaling of the unmerged data.  Unfortunately, you are at a tough resolution because you're hitting the water ring (high background) with your weakest data.  If you have partial phase information from some source, an anomalous difference Fourier will be your best bet to definitively detect the presence of a useful signal.

Good luck!


From: phenixbb-bounces at phenix-online.org [mailto:phenixbb-bounces at phenix-online.org] On Behalf Of ash.k at aol.com
Sent: Wednesday, November 14, 2012 2:41 PM
To: phenixbb at phenix-online.org
Subject: [phenixbb] Off topic: Anomalous signal

Dear all,

I am sorry for this off topic question in the bb. I have good looking but poorly diffracting (3.8-4 A) crystals of SeMet derivative. Mass spec confirmed that Se incorporation is 100% and I got a very good energy scan for Se too. I properly selected the peak, inflection and remote wavelengths for the data collection. But, I do not see anomalous signal in the data collected. Processing in HKL2000 does not show any resolution dependance of Chi square and also xtriage says that the anomalous resolution limit is only up to 8-9A. Is it something usual for the kind of diffraction I am getting or something else is going on? I have 5/200 methionine residues in the sequence. Worst case I can think of is that all the Met side chains are disordered !

Any help would be highly appreciated..

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