[sharp-discuss] SAD FOM centric reflections

[Zwart, Petrus H.]

The FOM for centrics is due to the Sim contribution of the partial
structure to the total phase distribution.

For example, if a substructure would consist of approximately 99% of the
protein, your centrics most likely would be correct, as the remaining 1%
of the scattering mass would not change the current phase very much.
On the other hand, if your substructure is close to 0% of the total
scattering mass, the correct centric phase can be either 0 or 180, with
almost equal probability. For more realistic cases, you would find that
one centric phase is slightly favored over the other. 

The contribution of the partial structure to the final phase probability
distribution is called the Sim contribution. For centric phases, it is
the only source of info you have. For acentric, this Sim contribution is
multiplied with a bimodal function. The partial structure skews the
resulting phase probabilities to one of the modes.

Hope this helps,

Cheers

Peter



 



> -----Original Message-----
> From: Carola Hunte [mailto:Carola.Hunte at mpibp-frankfurt.mpg.de]
> Sent: Thursday, February 10, 2005 8:41 AM
> To: sharp-discuss at globalphasing.com
> Subject: [sharp-discuss] SAD FOM centric reflections
> 
> Dear all, I was wondering whether there is relevant information in FOM
> of centric reflections in the SAD case.  In principal, centric
> reflections should not contribute to the anomalous phase information,
> but are they used in any way for SAD phasing in SHARP? Thanks for some
> insights, Carola
> 
> 
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