Hi Lin,
> I got the protein crystal structures from the PDB file.
> There are only residues and water in the PDB files.
>
> Why does the protein carry charges?
> Why aren't they electrically neutral?
Many residues are protonatable or deprotonatable. You should take a look at
an introductory biochemistry text book for an overview of amino acids, their
pKa values and thus protonation states at different pH values.
> What are their intrinsic counter ions ?
The counter ions are a function of the solution in which the protein exists.
Typically one uses sodium or chlorine in analogy to a saline solution
although other ions, such as potassium can also be used.
All the best
Ross
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Received on Sun May 24 2009 - 01:10:53 PDT
