Re: [ccp4bb] Differentiating bound Mn & Ca.

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Subject: Re: Differentiating bound Mn & Ca.
From: Eleanor Dodson ccp4 {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2007-04-16

In cases like this I use the S atoms to calibrate the peak height.
Of course it isnt definitive a) it is near the noise level, and b) peak
height is very dependent on B factor..
But the ratio might distinguish between an atom with an f" of 1.3 or f"=2.8

Eleanor

David Briggs wrote:
> Dear all.
>
> I have recently solved a structure in-house, 2.8A, CuKa.
> I have a metal ion bound very obvious hepta-valent co-ordination,
> which would suggest either Ca or Mn.
> Neither was present in the crystallisation setup, but there was some
> Mg around, which has contaminants of both Ca & Mn.
> At 2.8A, I don't really think I can reliably discriminate between
> 2.15A & 2.36A distances to coordinating atoms
> (http://tanna.bch.ed.ac.uk/newtargs_06.html
> ).
> The B factors for refined Ca are 18, and Mn 30. The B-factors of
> coordinating atoms vary from... 18 > 30 - so no help there.
>
> I have a nice clear 6sigma anomalous difference peak, but then,
> according to http://skuld.bmsc.washington.edu/scatter/ both Ca (f"
> ~1.3) and Mn (f" ~2.8) scatter anomalously at that wavelength.
>
> The obvious solution is go to a synchrotron and scan around the Mn
> edge and see what happens, however, whilst waiting for beam time, is
> there any way I could... oh I don't know, use the peak in my anomalous
> difference Fourier to figure out what anomalous signal would be
> required to generate a peak of that size - a sort of back-transform???
>
> Is this do-able, and if so, how would one go about it?
>
> Cheers,
>
> Dave
>
> --
> ---------------------------------------
> David Briggs, PhD.
> Father & Crystallographer
> www.dbriggs.talktalk.net
> iChat AIM ID: DBassophile
> ---------------------------------------
> Anyone who is capable of getting themselves made President should on
> no account be allowed to do the job. - Douglas Adams

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CCP4bb <-- 2007 <-- April 2007 <-- 16 April 2007

Previous message:
Subject: Team Leader in Structure-Based Drug Design
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From: Sreeram Mahesh mahesh {- at -} PHYSICS {- dot -} IISC {- dot -} ERNET {- dot -} IN
Date: 2007-04-16