[ccp4bb]: Can P43212 and P41212 be distinguished by anomalous signals?

["Q. Steven Xu" <qian@med-biophg.bu.edu>]

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Hi,

I have one sel-met cystal in tetragonal form, which turns out to be in
either P43212 or P41212 space group. It is supposed to have two
selenium atoms in the asymmetric unit. The MAD data set collected
form the crystal was subjected to SOLVE for MAD phasing. When I defined
the space group as P41212, the SOLVE gives a solution with only one
selenium site. All parameters (like overall Z score, f.o.m) are OK, except
that the peak height of the site is zero. In the case of P43212, two sites
show up as expected with very high peak heights (around 30). My question
is whether these two space groups can be distinguished by anomalous
signals, as shown by SOLVE?    

My another questions is, once I determine the space group, do I need to
flip the sites and try both possibilites? I remember somebody asked the
similar question before, but just can not find a clue in the archive.
sorry about that. Thanks in advance.

regards,
Q. Steven Xu
Dept. of Physiology and Biophysics
Boston Univ. School of Medicine
Tel: (617)638-4083
Fax: (617)638-4041
E-mail: qian@med-biophg.bu.edu