Chapter 27, Problem 27.31P

Interpretation Introduction

Interpretation:

The isoelectric points ($\text{pI}$) for the amino acids Aspartic acid and Glutamic acid has to be calculated.

Concept Introduction:

The isoelectric point of an amino acid is $\text{pH}$ at which the molecules in solution have net charge of zero.  The isoelectric point is calculated by using the formula

  $pI=\frac{1}{2}\left(pKa\alpha -COOH+pKa\alpha -N{H}_3{}^{+}\right)$

If the amino acids contains side chains, then for acidic side chain amino acids the ${\text{pK}}_{\text{a}}$ of ${\text{α-COO}}^{\text{-}}$ and the ${\text{pK}}_{\text{a}}$ of side chain ${\text{–COO}}^{\text{-}}$ can be calculated and for basic side chain amino acids, the ${\text{pK}}_{\text{a}}$ of ${\text{α-NH}}_{\text{3}}$ and the ${\text{pK}}_{\text{a}}$ of side chain ${\text{–NH}}_{\text{3}}$ can be calculated.