Chapter 5, Problem 3Q

Summary Introduction

To review:

The isoelectric point of the following tripeptide by assuming the pK_a (logarithmic acid, dissociation constant) values given in Table 5.2 (for table, refer to textbook).

Introduction:

A tripeptide is a chain of three amino acids connected to each other by a peptide bond. An isoelectric point (pI) is the pH, at which there is no net charge on the peptide and it is neutral in nature. When the titration of amino acids is carried out, there will be two pH values.

At low hydrogen ion or H⁺ concentration, the carboxyl end of the amino acid loses one H⁺ to become a negatively charged carboxylate group, which is acidic and is denoted by pK₁. At the other pH, it will be basic due to theaddition of anH⁺ to the amino end and denoted by pK₂. The average of pK₁ and pK₂ gives the value of the isoelectric point.