Chapter 17, Problem 51P

Interpretation Introduction

Interpretation:

The reason for why the $pI$ values of tyrosine and cysteine cannot be determined by the method described on $pKa$ value has to be explained.

Concept introduction:

The isoelectric point ($pI$) is the pH at which the amount of positive charge and negative charge on an amino acid becomes balanced.

The value of $pI$ is depends upon the $p{K}_a$ value of protonated amino group and $p{K}_a$ value of carboxyl group of an amino acid.

If the amino acid has ionizable side chain, then the $pI$ value is the average of $p{K}_a$ value of similarly ionizing groups.