I am looking for information regarding pH influence for the peaks shift in the low aliphatic region of the protein NMR spectrum.
In my research, I've performed fragment-based screening of the protein with NMR titrations and I've come across a problem. I've observed shifting of the peak around 0.4 ppm which was dependent on small pH changes (in the range of approx. 0.5). At first, I've taken this as the binding of my fragment but the change was reversed just by the adjustment to the initial pH.
I am wondering why, in this not ionizable area, there is such big sensitivity for pH. I would be grateful for any hints regarding this topic.
Dear Ewa,
The shift may be not due to direct protonation/deprotonation when altering the pH, but it may be close in space to a residue whose protonation state is changing with those changes of pH.
Alternatively, you could be observing the effect of protonation/deprotonation of a chemical group of a residue in a different H of that same residue. This has been observed in effect of protonation/deprotonation of reduced cysteine residues in its Hbeta.
I hope this helps.
Jose
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