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RE: [ccp4bb]: Q: Sign of anomalous difference out of Scalepack



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On Fri, 16 Aug 2002, Vajdos, Felix wrote:

> This is exactly what happened to me a few years back with data from a
> synchrotron beamline.  The clincher was the fact that the electron density
> maps revealed perfect left-handed helices. 
> 
> Reversing the sign of DANO and the changing to the other possibility of
> space group [P4(3,1)2(1)2] did the trick.  For data collected on
> commercially available detectors, though, one should not have to worry about
> it.  

enantiomorphic space groups are a special case. reversing the sign of DANO 
and changing to the opposite enantiomer are 2 separate things. the first 
should not be necessary unless your data collection/processing software 
has something set wrong.  the second may occur for any space group with an 
enantiomeric pair, such as P4(1)22 and P4(3)22, and the left-handed 
helices are your clue that you picked the wrong enantiomer.

cheers, 
=======================================================================
Life is a struggle, not against sin, not against the Money Power, not 
against the malicious animal magnetism, but against hydrogen ions.
                                                - H.L. Mencken
=======================================================================
                        David J. Schuller
                        modern man in a post-modern world
                        MacCHESS, Cornell University
                        djs63@cornell.edu