RE: Solvent correction ?

[Jens Petersen <jens@obed.biochem.ualberta.ca>]

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This is in part a responce to S.Ravichandran and Edward Berry
regarding solvent correction.

There is indeed a difference between the "exponential scaling model" used
in REFMAC using Babinet's principle and the "mask model" used in CNS and
XPLOR.

The "exponential scaling model" assumes that the structure factors of the
bulk solvent electron density are directly proportional to the structure
factors of the protein electron density but with opposite phases. This is
only a good approximation at very low resolution ~15 A.

In contrast the "mask model" does not have any assumption of the phase
relationship between the protein structure factors and the bulksolvent
structure factors.

The two models are therefore not two different ways of coming to the same
result. As Edward Berry states.


I am essentially repeating what have allready been stated before.
An excelent treatment of this topic can be found in the September 1997
Issue of the CCP4 NEWSLETTER by Dirk Kostrewa which can be downloaded
directly from the CCP4 homepage.

-- 
Jens F.W. Petersen, Ph.D
Department of Biochemistry
4-25 Medical Sciences Building
University of Alberta
Canada T6G 2H7
Phone  (780) 492 2422
Fax    (780) 492 0886
Email jens@manitou.biochem.ualberta.ca