Dear Derek,
we are using the quick-soak method frequently at the BESSY-MX beamlines.
So far we were able to obtain phase information in terms of MAD/SAD-
phases in all cases which we tried. The starting set-up is the screen
over the 4-6 most successful heavy atom compounds at 5-10mM
concentration and 10-20 min soaking time.
If you follow the soaking under a transmissive light microscope like the
Leica MZ7.5, you can receive quite intriguing visual feedbacks from your
experimental set-up, including the bending of large crystal face areas
towards the crystal center due to the large osmotic pressure at the
beginning of the process an others. Those observations might provide you
further information for the optimization loop which will be confirmed by
the detection of an anomalous signal after the peak-dataset.
3-8 of such fast feedback loops could be carried out within a 8h
beamtime shift and led to interpretable electron densities.
So, I regard this method as a very powerful alternative, where the
availability of SeMet-crystals is limited.
Best regards,
Uwe
Derek Logan schrieb:
Hi,
I'd like to find out how successful the "quick soak" method for heavy
atom derivatisation proposed by Radaev and Sun:
Sun PD, Radaev S, Kattah M. Generating isomorphous heavy-atom
derivatives by a quick-soak method. Part I: test cases. Acta Cryst.
2002. D58:1092-1098.
has been in comparison to the "classical" method of longer soaks at
low concentrations of heavy atom compound. The method was quite
successful in our hands a few years ago but (fortunately?) it's
becoming increasingly rare that we use heavy atoms. I understand that
evidence will necessarily be anecdotal, but let's not let that stop us.
Derek
--
Derek Logan tel: +46 46 222 1443
Associate professor fax: +46 46 222 4692
Molecular Biophysics mob: +46 76 8585 707
Lund University
Box 124, Lund, Sweden
--
_______________________________
Dr. Uwe Müller
BESSY-MX group
BESSY GmbH
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Phone: +49-(0)30-6392 4974
Fax : +49-(0)30-6392 4975
email: [EMAIL PROTECTED]
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