In the case of subtilisin, soaking the crystal in acetonitrile
removed very little water and only a few (roughly 10) acetonitrile
molecules were found bound to the protein (D. Ringe and coauthors, PNAS,
~1994). So I question whether DMF will do any better than acetonitrile at
removing waters.
Chris Halkides
*******************************************************************************
We've tried a Karl Fischer titration to measure water which was subtracted
>from the overall lyophilized weight and still it came back high by 20%.
>I'm not sure if extraction with DMF before moisture analysis is able to
>strip protein bound water off. Do you know?
>
>The counter-ion effect is something we are analyzing. We have desalted the
>protein into H20 so the contribution of unbound salt is not there. The Pi
>of the protein I believe is around 5 and the pH of the desalted material
>into H20 is around 7. We've sent the protein for sodium analysis to
>analyze this counter-ion effect you mentioned.
>
>In you experience, what contribution weight does this counter ion effect
>have vs. the bound H20 effect? Are we on the right path? Thank you for
>your help. We will try to "dry" the protein down further.
>
>Best regards, John
Christopher Halkides
Dept. of Chemistry, UNCW
601 S. College Road
Wilmington, NC 28403-3297
(910) 962-7427