(a) What is the pI (isoelectric point) of the amino acid arginine (pK1=2.2, pK2=9.8, pK3=12.5)?
[Hint: draw a table with different pH range to identify the pH range in which arginine has a neutral charge].
(b) Based on the calculations, what can you infer about the pI value of an amino acid with more than two ionizable groups (e.g., arginine has two amino groups and a C-terminal carboxylate group)?
[Hint: check pKa values of which ionizable groups are contributing to calculating the pI].