How to get the solvation No. from accessible surface

From: Massimo Marchi <marchi -AatT- villon.saclay.cea.fr>
Subject: How to get the solvation No. from accessible surface
Date: Fri, 9 Nov 2001 17:37:19 +0000 (WET)

Dear all,
 I have seen in literature that to get the total number of water
 molecules solvating a protein, some people compute the solvent
 accessible surface (in some way) in A^2 and divide by 15 A^2. Does
 anybody know the origin of this "magic" number?
 Thank you beforehands
 Massimo MARCHI
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 = Dr. Massimo MARCHI                      marchi -AatT- villon.saclay.cea.fr   =
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 = Centre D'Etudes de Saclay, Section de Biophysique                     =
 = Gif-sur-Yvette, Paris, FRANCE                                         =
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