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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