Can I be dogmatic about this ?
Multiwavelength anomalous diffraction from Hendrickson (1991) Science
Vol. 254 no. 5028 pp. 51-58
Multiwavelength anomalous diffraction (MAD) from the CCP4 proceedings
http://www.ccp4.ac.uk/courses/proceedings/1997/j_smith/main.html
Multi-wavelength anomalous-diffraction (MAD) from Terwilliger Acta
Cryst. (1994). D50, 11-16
etc.
I don't see where the problem lies:
a SAD experiment is a single wavelength experiment where you are using
the anomalous/dispersive signals for phasing
a MAD experiment is a multiple wavelength version of SAD. Hopefully one
picks an appropriate range of wavelengths for whatever complex case one has.
One can have SAD and MAD datasets that exploit anomalous/dispersive
signals from multiple difference sources. This after all is one of the
things that SHARP is particularly good at accommodating.
If you're not using the anomalous/dispersive signals for phasing, you're
collecting native data. After all C,N,O,S etc all have a small
anomalous signal at all wavelengths, and metalloproteins usually have
even larger signals so the mere presence of a theoretical d" difference
does not make it a SAD dataset. ALL datasets contain some
anomalous/dispersive signals, most of the time way down in the noise.
Phil Jeffrey
Princeton
On 1/18/12 12:48 PM, Francis E Reyes wrote:
Using the terms 'MAD' and 'SAD' have always been confusing to me when
considering more complex phasing cases. What happens if you have intrinsic
Zn's, collect a 3wvl experiment and then derivatize it with SeMet or a heavy
atom? Or the MAD+native scenario (SHARP) ?
Instead of using MAD/SAD nomenclature I favor explicitly stating whether
dispersive/anomalous/isomorphous differences (and what heavy atoms for each )
were used in phasing. Aren't analyzing the differences (independent of
source) the important bit anyway?
F
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Francis E. Reyes M.Sc.
215 UCB
University of Colorado at Boulder
