I have been given the following table of the pKa associated with each ionizable group in the peptide 'Asp-His-Arg'
Asp: pKa NH3+: 9.9, pKa COOH: 2.0, pKa Side Chain: 3.9
His: pKa NH3+: 9.3, pKa COOH: 1.8, pKa Side Chain: 6.0
Arg: pKa NH3+: 9.0, pKa COOH: 1.8, pKa Side Chain: 12.5
I have worked out the overall charge to be +1 at pH 7 (though this could be incorrect), but have now been asked to calculate the overall charge at pHs: 1.8, 6, 7, 9.9
How do I do this?? Any help would be greatly appreciated, thanks.