Re: [ccp4bb]: Anomalous data?

[Thomas Edwards <edwards@inka.mssm.edu>]

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On Saturday 28 April 2001 20:27, you wrote:
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> Hello,
>
>  We recently collected MAD data sets at CHESS(F2) on a
> protein crystal soaked in an Os solution.  The EXAFS scan before the
> data collection showed the presence of Os atoms in
> the crystal.  Now when we use scalepack to find how good
> the anomalous differences are, the output says the differences
> are zero!  What does this mean?  Could random binding of Os
> give such a result?  Thanks for any ideas/tips.
>
> Hemant

Hemant: 
this happens alot!!

Things to check:
1) did you wash your crystal in new cryo soln before freezing? If not you 
froze Os in the loop and that will give you signal. 
2) you need to soak the crystal in cryo after Os soak for long enough to get 
the Os out of the solvent in the crystal too.
3) you could still have had some random Os binding, sorry about that.

A very useful method for pre-screening heavy atoms without having to use 
crystals (or even shoot at any) is presented in:
Boggon TJ, Shapiro L.
Screening for phasing atoms in protein crystallography
Structure Fold Des 2000 Jul 15;8(7)

Ed