Amino Acids and the Henderson-Hasselbalch Equation Isoelectric Points

Amino Acids and the Henderson-Hasselbalch Equation Isoelectric Points 

According to the Henderson-Hasselhalch equation (Sections 15.3 and 18.5), if we know both the pH of a solution and the pATg of an acid HA, we can calculate the ratio of [A ] to [HA] in the solution. Furthermore, when pH = pXg, the two forms A and HA are present in equal amounts because log 1 = 0. 

To apply the Henderson-Hasselhalch equation to an amino acid, let s find out what species are present in a 1.00 M solution of alanine at pH = 9.00. According to Table 19.1, protonated alanine [ H3NCH(CH3)C02H] haspA ai = 2.34 and neutral zwitterionic alanine [ H3NCH(CH3)C02 ] has = 9.69  

Since the pH of the solution is much closer to pJ az than to p ai. we need to use pA a2 for tbe calculation. From the Henderson-Hasselbalch equation, we have  

CHAPTER 19 biomolecules amino acids, peptides, and proteins 

---

Amino Acids, the Henderson-Hasselbalch Equation, and Isoelectric Points... 

---