Hello!
The question is what happens with the charge of n-end aminoacid if the protein is not surrounded by water molecules or just partially surrounded by them. For example, in crystal, or inside lamella. Protonation state of amine is NH3 in water at pH 7 bacause of the H+ ion presence and should not change. But if the amine group has no more contact with water and is in close contact with positively charged molecules, would it cause a loss of one hydrogen?
Good question! Most proteins/peptides prefer slightly acidic conditions (where they are most active). Thus the terminal N end would be protonated along with the terminal C end (carboxyl group).
I presume these ends would become deprotonated and the protein inactive in a slightly alkaline lyophilization condition.
It is known that the N-terminus of a peptide or protein is less basic than other amino groups in these molecules. However, the pka value of a group can be highly influenced by its environment, which might be the case in your experiment. In proteins, the N-terminus shows a pKa of 7.7 ± 0.5 (see paper).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2708032/
Thank you all!
In my case protein is not fully in water solution, but exposed on the graphite surface. C-end is amidated and neutral. Other aminoacids are neutral too, the only question is in the N-end charge and protonation state...
- Badges
- Science topic
- Similar topics
- Biological Science
- Biochemistry
- Biomolecules
- Peptides