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<TITLE>Re: [RASMB] hydrated vs. anhydrous MW</TITLE>
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<BLOCKQUOTE><FONT COLOR="#800000">Hi Karl<BR>
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Sedimentation equilibrium measure the <I>buoyant</I> mass of a protein in (normally aqueous) solution. Archimedes and all that. With a minor reservation which in practice has little practical effect (see my communication of 2 days back) the water associated with a protein has the same density as free water. So - just as the buoyant mass of a boat is unaffected by any water that gets stuck to it (a bit hypothetical that one - but maybe it could go into a jelly form!), so the mass estimate from sedimentation equilibrium is unaffected by water bound.<BR>
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That applies to the <I>equilibrium</I> state. Transport methods - e.g. sedimentation velocity, dynamic light scattering - are very much affected by any bound component which increases the hydrodynamic radius.<BR>
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All best<BR>
<BR>
Arthur Rowe<BR>
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Arthur J Rowe<BR>
Professor of Biomolecular Technology<BR>
NCMH Business Centre<BR>
University of Nottingham<BR>
School of Biosciences<BR>
Sutton Bonington<BR>
Leicestershire LE12 5RD UK<BR>
<BR>
Tel: +44 (0)115 951 6156<BR>
+44 (0)116 271 4502<BR>
Fax: +44 (0)115 951 6157<BR>
email: arthur.rowe@nottingham.ac.uk<BR>
arthur.rowe@connectfree.co.uk (home)<BR>
Web: www.nottingham.ac.uk/ncmh/business<BR>
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Dear RASMBers,<BR>
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The typical hydration estimate for proteins of 0.3 grams water bound per gram protein would seem to predict that proteins will have molecular weights about 1.3 times larger than predicted by their primary sequences, yet this does not seem to be observed experimentally by sedimentation equilibrium techniques. Can someone help me understand why this is not observed?<BR>
<BR>
Karl Maluf<BR>
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