Chapter 21.4, Problem 13P

(a)

Interpretation Introduction

Interpretation:

The percentage of α-amino group of lysine will be protonated at its $pI$ has to be calculated.

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 no ionizable side chain, then the $pI$ value is the average of $p{K}_a$ value of protonated amino group and $p{K}_a$ value of carboxyl group of that 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.

The $pI$ value of lysine is 9.87.

(b)

Interpretation Introduction

Interpretation:

The percentage of β-amino group of lysine will be protonated at its $pI$ has to be calculated.

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 no ionizable side chain, then the $pI$ value is the average of $p{K}_a$ value of protonated amino group and $p{K}_a$ value of carboxyl group of that 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.

The $pI$ value of lysine is 9.87.