Looking at the fit in your attached JPEG it's clear that you won't get
sensible Kds for this peak at least.
1 The chemical shift changes are tiny, so you'd have to question whether
this is a real ligand effect, or a systematic feature such as change in
conditions (pH, temp, ionic strength, protein conc, co-solvent, etc.).
2 if this peak is revealing anything more than a systematic feature, your
titration either doesn't go far enough to get anywhere near saturating
your protein, or your Kd is so low (binding so tight) that all your
ligand is binding to protein at each point. From what you said about
your setup the former would be more likely!
Walter Chazin's lab have a great web page on the pitfalls of getting Kds
from spectroscopic titrations (of any sort)
http://structbio.vanderbilt.edu/chazin/wisdom/kdcalc.htm
Brian
PS For Wayne et al. - what's the origin of the function with the "+ C" in?
--
Dr. Brian O. Smith ---------------------- B Smith at bio gla ac uk
Division of Molecular & Cellular Biology,
Faculty of Biomedical & Life Sciences,
Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, UK.
Tel: 0141 330 5167/6459/3089 Fax: 0141 330 4600
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